(written from a Production point of view)
The USS Discovery crew is intrigued by new addition Lieutenant Ash Tyler. Sarek seeks Burnham's help, rekindling memories from her past. Admiral Cornwell questions Lorca's tactics.
On the USS Discovery, Burnham and Tilly are running together and discussing goals in Starfleet. Elsewhere, Lorca and Tyler are running a tactical drill in the holodeck while Lorca asks Tyler about himself. Lorca tries to check his story, but has already done most of the work and offers him chief of security on the ship.
On the Vulcan ship, Sarek's aide injects himself and changed the ship's heading, revealing he knows about the mission. He declares Sarek cares too much about humans and the Federation, and wants to sacrifice himself to kill Sarek as a rallying cry "to those who value logic above all."
Burnham and Tilly eat after their workout, and Burnham micromanages her food choices. Tilly sees Tyler and excitedly goes to sit with him to meet him. Burnham is suspicious of the rumors about him. When she shakes his hand, however, she feels Sarek's pain and finds herself in the memory of herself, Sarek and Amanda when she found out she didn't get in to the Vulcan Expeditionary Group. Suddenly, Sarek turns to her abruptly in the memory and pushes her out.
She wakes up in sickbay, and explains the memory and the bombing. Her mind meld with Sarek saved her but also gave her part of his katra. She asks Lorca to help her. Admiral Terral confirms Sarek's mission and location. He promises to find him.
They arrive. Lorca orders probes to send into the nebula, but Burnham suggests using herself. With Stamets, they discuss an augmentation to her mind. After they leave, Lorca is informed of a visit by Cornwell, who is furious with his decisions. Lorca gets out a drink to talk.
On the shuttle into the nebula, Tilly is trying to talk through being nervous, and tries to get Burnham to talk. Tyler cuts in to say they're in position, and Burnham lies down with the interface. She finds herself back in the memory, when her mother gave her a copy of Alice's Adventures in Wonderland. Burnham confronts Sarek and they fight. Tyler orders it stopped and heads back to the ship. Burnham protests and Tyler reluctantly lets her try again.
Meanwhile, Cornwell and Lorca relive a memory of their past with a drink. Cornwell turns to the present, and expresses concern about Lorca, especially since the incident on the USS Buran. Lorca still insists he is OK and turns the conversation.
Back in Sarek's memory, Burnham confronts Sarek on what he's hiding from her. He finally shows her the memory of him hearing the news of her rejection. The Vulcan expresses concerns about admitting not only one but two non-Vulcans (referring to Spock), but does permit one, forcing Sarek to make a choice. He decided to admit Spock and did not tell Burnham the full story. He then admits he felt shame and allows her to find him. He gets up on his ship and turns on his transponder. Tyler soon finds him.
Cornwell is in bed with Lorca, and, as he sleeps, touches a scar on his back. On instinct, Lorca jumps and holds a phaser to her, then backs off and apologizes. This is the last straw for Cornwell, now convinced he is not stable enough to handle Starfleet's greatest weapon. She leaves, promising that he will not have it for long.
Lorca goes to sickbay to learn about Sarek's rescue. When Burnham thanks him for the mission, Lorca says he did the mission for her, and also offers her a science station post on the bridge. She thanks him again. Burnham then goes inside to confirm that Sarek remembers what happened between them. He doesn't talk about it, but Burnham promises they will one day.
Cornwell sees Lorca off before her mission, and he wishes her well.
In the mess hall, Tyler invites Burnham to chat. Burnham admits she will never get from Sarek what she wants as a father. They introduce each other again.
Cornwell meets with the Klingons on Cancri IV. Led into a room hosted by some of the population's elders, Cornwell begins to greet the Klingons. Just after she completes an introduction, however, the Klingons kill the security officers, leaving Cornwell. Kol's holographic image appears and, in Klingon, says he is pleased they captured her instead of Sarek. He promises cloaking technology to Dennas for capturing her. In English, he tells Cornwell looks forward to meeting her.
Saru informs Lorca of Cornwell's abduction. Lorca, uncharacteristically, orders him to get direction from Starfleet Command instead of going after her himself. He takes a look at the stars, with a phaser now tucked behind in his pants.
"May I inquire as to the nature of our diplomatic mission?"
"Allow me to be diplomatic and ask that you do not. In times of crisis, ignorance can be beneficial."
- - V'Latak and Sarek, on Sarek's mission
"Everyone applying to the Command Training Program will be smart. Personality doesn't count."
"That's just something people with no personality say. Wait... which... which in no way means you... you absolutely have a personality!"
"6.5 seconds is not an arbitrary number. Your new time will earn you a physical endurance commendation. Today your goal is 6.5 seconds. Then, getting a transfer on a Constitution-class like the Enterprise. After that, first officer track. See your path. Stay on it. Reach your destination. Cadet to captain; just like that."
- - Michael Burnham and Sylvia Tilly, on how Tilly can become a captain in the future
"Don't apologize for excellence. I want my chief of security to shoot better than I do."
- - Gabriel Lorca
"This mission does not reflect true Vulcan ideology."
"You are one of them. A fanatic."
"Your fascination with humans can no longer be tolerated. Your obsession has blinded you to the truth. Humans are inferior. My sacrifice will be a rallying cry to those who value logic above all. Vulcans will soon recognize and withdraw from the failed experiment known as the Federation."
- - V'Latak and Sarek, as V'Latak attempts to kill Sarek in a suicide attack
"Computer, green juice, extra green."
"Computer, cancel that order. That's hardly the correct ratio of protein, carbohydrates, and fat. Computer, three egg-white breakfast burrito with black beans."
"Make it two."
"Computer, add salsa."
"Computer, add roasted tomato salsa. Cooked tomatoes are a great source of lycopene. Remember that."
"Oh my God, you are so scary."
- - Sylvia Tilly and Michael Burnham
"Clearly, your trip down the mycelium path has lightened your mood, lieutenant."
"Once you're past getting stabbed by needles, it's pretty great."
- - Gabriel Lorca and Paul Stamets
"I can sense that Sarek is unconscious. I want to use this mimd-meld to wake him up so he can activate his ship's transponder."
"Right, like a psychic hit of speed."
"I was thinking an adrenaline shot, but okay."
- - Michael Burnham and Paul Stamets
"You chose Spock over me, didn't you? You were forced into that decision, why not just tell me the truth?"
"Spock went against my wishes, and joined Starfleet over the Vulcan Expeditionary Group. The choice I made merited nothing. What would be gained by telling you that?"
"Instead, you made me believe I failed you. You manipulated me. Do you have any idea what living with that lie did to me?"
"I did not. But I do now."
- - Michael Burnham and Sarek, after Sarek reveals the truth on why Burnham was rejected from the Vulcan Expeditionary Group
"You sleep with a phaser in your bed, and you say nothing's wrong?! All these months I have ignored the signs, but I can't anymore. The truth is you are not the man I used to know, and I'm not like the rest of them at Starfleet, blinded by your victories! You lied on those psych evaluations, and you did it so brilliantly, you fooled everyone."
- - Katrina Cornwell
"You said it yourself, we're at war. I can't leave Starfleet's most powerful weapon in the hands of a broken man."
"Don't take my ship away from me! She's all I got. Please, I'm begging you. Now, you're right. It's been harder on me than I let on, and I lied about everything, and I need help."
"I hate that I can't tell if this is really you."
- - Katrina Cornwell and Gabriel Lorca, on Lorca's ability to command the USS Discovery
"Help me understand what you did. It could make us grow closer, not further apart. That's what families do."
"Technically, we are not related."
"You can do better. But I won't push you. We'll have this conversation one day. Father."
- - Michael Burnham and Sarek, on Sarek's memories
"I gave you bad advice. There are a million ways to get to the captain's chair. Find your own."
- - Michael Burnham and Sylvia Tilly, as she continues Burnham's training regime
- In Greek mythology, Lethe was both a river in the underworld and the Greek goddess of forgetfulness and oblivion. There was also a character named Lethe in TOS: "Dagger of the Mind", and the Letheans were a race introduced in another episode that Joe Menosky was involved in, DS9: "Distant Voices".
Story and script
- This was the first episode of Star Trek to be written by Joe Menosky since VOY: "Unimatrix Zero, Part II" in 2000.
- The script of this episode called for a Vulcan ship to appear but wasn't very specific about it. "The script just said, 'Vulcan ship' and that was it," recalled Goran Delic, who took on the task of designing the vessel. "There was no description. I knew that it was to be used by the Vulcan ambassador and that it should look slick and powerful in a Vulcan way, but that was it. The description was very vague." (Star Trek: Discovery Designing Starships, p. 110)
- According to Admiral Cornwell actress Jayne Brook, this episode originally was to have concluded with the admiral being killed in the Klingon massacre. Concerning how the writers altered the scene, Brook later remembered, "They thought she would die in that massacre. But [then …] they were like, 'Hmm, maybe we'll have them be taken prisoner instead.'" 
- Executive Producer Gretchen J. Berg commented that even having Admiral Cornwell use her phaser against the Klingons during the incident "would have complicated the story for the writers." (AT: "Lethe")
- In AT: "Si Vis Pacem, Para Bellum", Jayne Brook talked about a moment from this episode, where Lorca and Cornwell reminiscence about watching the Perseids meteor shower. She remembered this to have been in Iowa, even though the episode gave no location.
- With the addition of this episode, Mia Kirshner became the fifth actress to portray the character of Amanda Grayson. Jane Wyatt originated the role in TOS: "Journey to Babel", Majel Barrett voiced the character in TAS: "Yesteryear", Cynthia Blaise played a young Amanda in Star Trek V: The Final Frontier, and Winona Ryder portrayed her alternate reality counterpart in the 2009 film Star Trek (as well as, in a deleted scene from that movie, the prime-universe version of the character).
- The scenes on Vulcan were filmed at the Aga Khan Museum in Toronto. 
- The jogging scene took eight hours to film. The set of the Discovery's corridors was only long enough to accommodate ten seconds of dialogue. To shoot the scene, cameras rolled on segways while actresses Sonequa Martin-Green and Mary Wiseman ran through the set. (AT: "Lethe")
- The holographic battle simulation took twelve hours to shoot; Jason Isaacs developed most of the fight choreography himself, basing it on his previous film experience. (AT: "Lethe")
- Sarek actor James Frain joked that, to prepare for the filming of their Suus Mahna fight scene together, he and Sonequa Martin-Green "trained for months on a remote Himalayan mountaintop with Shaolin monks," and Gretchen Berg then humorously feigned surprise at After Trek host Matt Mira considering that was probably "an excessive use of budget." (AT: "Lethe") In reality, the fight was devised by Stunt Coordinator Christopher McGuire and Fight Co-ordinator Hubert Boorder. (Q&A at "Si Vis Pacem, Para Bellum" screening, Millbank Tower, London, UK, 5 November 2017) Explained Frain, "We rehearsed with the stunt guys who designed the fight. And then, on the day, they put me and Sonequa together, and it was like, 'Go.' They were like, 'Oh! You don't have any experience at all?' And I'm like, 'Not really.'" (AT: "Lethe") Martin-Green, on the other hand, had a passion for and a wealth of experience of stage combat that she was able to bring to the fight scene. She said about how she and Frain tackled the scene, "We did not get a lot of time [.…] We did not rehearse together for that fight. I had one forty-five-minute rehearsal for that fight, and I think he had two forty-five-minute rehearsals. And then the first time we fought together was on camera. So, we found it together. We sort of dove in [.…] Obviously, he has everything to do with the success of that fight too; he was awesome. So, we were just like, 'Alright, well, we gotta do this! Here we go!' you know, so it was great." (Q&A at "Si Vis Pacem, Para Bellum" screening, Millbank Tower, London, UK, 5 November 2017)
- After accepting the challenge of designing Sarek's cruiser, Goran Delic produced a series of concept illustrations that showed how the craft would look when it took off from Vulcan. (Star Trek: Discovery Designing Starships, p. 117)
- During the opening scenes where Michael Burnham and Sylvia Tilly are jogging through a corridor, an alternate version of the DIS opening theme can be heard playing in the background. This composition replaced a temporary piece of music while the episode's score was being developed. Composer Jeff Russo reflected, "We were spotting the episode [….] There was some temp in there. Like, maybe Tilly was listening to some music or something, and I don't remember what it was. So, I said to Alex… I was like, 'What if I were to do, like, an eight-bit electronic version of our main theme. You know, like, sneak the main theme in, in this instance, and it sounds like… you know, doesn't sound like our score, because it's not very like our show to have this moment, but it's still melodically from our score.' And he was like, 'Well, let me hear what you hear.' So, I sort of went and did a version of it that was, you know, very just percussive, eight-bit-sounding, synthetic-sounding, and it ended up working really well in the scene."  In the soundtrack album Star Trek: Discovery - Season 1, Chapter 1, this music cue is called "Persistence". Although the vinyl LP Star Trek: Discovery - Season 1, Chapters 1 & 2 was subsequently released, this track wasn't included in it.
- This episode takes place less than a week after the events of DIS: "Choose Your Pain".
- In the series run of DIS, this was the first appearance of both Dennas and Sarek in the flesh. Sarek previously appeared via flashbacks, holo-communicator, and long-range psychic contact in the series premiere two-parter "The Vulcan Hello" and "Battle at the Binary Stars", whereas Dennas appeared via holo-communicator in "Battle at the Binary Stars".
- This episode also features the first mention of Constitution-class starships, specifically the USS Enterprise, in the series.
- The episode reveals that there are Vulcan extremists who seek a society with greater adherence to logic, and who wish Vulcan to leave the Federation. This recalls Vulcan extremists of differing ideologies in both Enterprise and The Next Generation (in "Gambit, Part II"). Although Vulcan extremists who rejected unity among Federation species seemed to have been crushed in ENT: "Kir'Shara", this episode shows they continued to exist thereafter.
- Although this episode includes some footage of Amanda Grayson set chronologically earlier than her first appearance in TOS: "Journey to Babel", young versions of the character also appeared in Star Trek V: The Final Frontier and TAS: "Yesteryear".
- Captain Lorca is seen sitting in the captain's chair for the first time in the series.
- The multicolored holographic display Lorca is studying when Cornwell arrives later reappears in "Magic to Make the Sanest Man Go Mad" and mid-first-season finale "Into the Forest I Go". The latter episode establishes it as a display of parallel universes.
- In her interaction with Sarek's memories, Burnham learns how Sarek failed her, and viewers learn part of why Sarek was so upset at Spock entering Starfleet (another, previously established aspect of Sarek's disappointment at Spock's career choice being that Sarek had wanted Spock to instead attend the Vulcan Science Academy). Sarek sacrificed Burnham's acceptance to the Vulcan Expeditionary Group for Spock, as the director of the group, anticipating Spock's future application but viewing both Burnham and Spock as "half-Vulcans", would only accept one of the two. When Spock chose otherwise, Sarek realized he had hurt his adopted daughter for nothing and thus carried a great sense of shame.
- When Captain Lorca bids farewell to Admiral Cornwell, he tells her, "May fortune favor the bold, admiral." In DS9: "Favor the Bold", Captain Sisko states, during a fleet-wide hail, "There's an old saying: fortune favors the bold." 
Reception and aftermath
- AT: "Lethe" discusses the making of, and events in, this episode.
- None of the DIS writers were aware that t-shirts labeled "DISCO" were being created or used until they saw some of the footage from this episode. (AT: "Lethe")
- Four weeks prior to this episode being released, James Frain revealed, "There may be a bit of a showdown between Sarek and another Vulcan." Frain also teased, "There might be a scene with some other Vulcans." (AT: "O Discovery, Where Art Thou?") A week prior to this installment's release, Mary Chieffo and Kenneth Mitchell revealed, on AT: "Choose Your Pain", that Dennas would reappear in this episode. The same episode of After Trek debuted the mess hall scene wherein, after Tilly introduces Burnham to Tyler, Burnham falls to the floor and experiences a vision of a distressed Sarek lying on the ground.
- Gretchen J. Berg stated that she "loved" that this episode allowed James Frain an opportunity to show off his Vulcan martial arts. She additionally remarked about that fight scene, "It's beautiful, it looks fantastic," and approved of the look of Vulcan in this episode. Berg thought highly, too, of how this episode further developed the relationship between Burnham and Tilly. "I love the fact that also that friendship is really blossoming and growing between the two of them [....] I also love that Tilly is like, 'Hey, there's a cute guy. We're gonna go check him out,' and then when she sees that there's chemistry between the other two, she's like, 'Alright! Go for it, you crazy kids.'" (AT: "Lethe")
- Co-Executive Producer Jordon Nardino found this episode to be highly moving, emotionally. "Episode six, I bawled," he admitted. "I've seen it three times now, and I bawl every single time. Burnham's backstory with Sarek kills me, and the revelation of the choice he had to make between Spock and Burnham and that he's been holding that in his whole life and he's carrying like a weight to his grave." ("Star Trek: Discovery: The Voyage of Season 1", DIS Season 1 DVD & Blu-ray special features)
- Matt Mira was wowed by the scene in which Burnham meets Ash Tyler for the first time then falls down and sees a vision of Sarek. (AT: "Choose Your Pain") When he first heard about the notion of a Vulcan fight scene in this episode, Mira, amazed, declared the idea was "hot." (AT: "O Discovery, Where Art Thou?") Once he saw the episode, he opined that that scene "looks amazing," and that Vulcan "looks gorgeous in this." Although he had always imagined Vulcan as being too hot to visit, this installment's depiction of the planet changed his mind about that. Mira also thought it "fun" that Burnham was shown taking social advice from Tilly, as she seemed to be the most socially awkward person aboard the Discovery. (AT: "Lethe")
- Evidently, a clip from this episode was subsequently reused in "The Wolf Inside".
- 30 September 2017: Title publicly revealed 
- 22 October 2017: Premiere airdate on CBS All Access
- 23 October 2017: International release date (outside Canada and the USA)
Links and references
- Sonequa Martin-Green as Michael Burnham
- Doug Jones as Saru
- Shazad Latif as Ash Tyler
- Anthony Rapp as Paul Stamets
- Mary Wiseman as Sylvia Tilly
- Jayne Brook as Katrina Cornwell
- Wilson Cruz as Hugh Culber
- James Frain as Sarek
- Mia Kirshner as Amanda Grayson
- Kenneth Mitchell as Kol
- Conrad Coates as Terral
- Emily Coutts as Keyla Detmer
- Julianne Grossman as Discovery Computer
- Luke Humphrey as V'Latak
- Clare McConnell as Dennas
- Sara Mitich as Airiam
- Oyin Oladejo as Joann Owosekun
- Damon Runyan as Ujilli
- Jonathan Whittaker as Vulcan Director
- Tim Cody
- Steve Gagne as Stunt Klingon
- Jordan Lockhart as Vulcan
- Serena Thompson as Vulcan
- Unknown actors as
ability; adjunct; adrenaline shot; alkaloid; Alice's Adventures in Wonderland; amino acid; antioxidant; athletic ability; black bean; book exchange; breakfast; Buran, USS; burrito; Cadet; Cancri; Cancri IV; Cancri system; carbohydrate; cargo bay; chief of security; comet; Command Training Program; Constitution-class; Cornwell's cruiser; director; DSC 01; Dock 3; Doctari Alpha; Edison, USS; egg; elder; emergency beacon; emergency life support; Engle-class; Enterprise, USS; Eridani D; eugenic manipulation; Europa, USS; experience; fat; fiefdom; flight plan; fortune cookie; French fries; GNDN; graduation day; Grazer; green juice; green tea; groovy; hamburger; hand-to-hand combat; hit; hologram battle simulation; host; humiliation; IDIC; ideology; intelligence; Interstellar Import; Issaquah Elementary; katra; ketchup; Klingon Bird-of-Prey; L'Rell's battle cruiser; logic extremist; Landry, Ellen; Logan; logic; lycopene; martial arts; meeting; mentor; metrics; Molina; moons of Grazer; mycelium spore; neural enhancer; observation deck; offload team; Perseids; personality; physical-endurance commendation; protein; psych evaluation; radioactivity; Rause; rescue mission; salsa; Sarek's cruiser; SarekVision; science specialist; scuttlebutt; Seattle; single malt; soul; soul graft; speed; Spock; Starfleet Academy; Starfleet Command; superhighway; synthetic mind meld augment; teacher; third grade; tomato; transponder; transpo drill; Tyler's father; Tyler's mother; Vulcan; Vulcan cruiser (cruisers); Vulcan Expeditionary Group; Vulcan High Council; Vulcan Learning Center; Vulcan gong; Vulcan lute; mind meld; Vulcan Science Academy; Webb; Wee Bairns; Wells; Wilson; worker bee; Yridia; Yridia Nebula
- "Lethe" at StarTrek.com, the official Star Trek website
- "Lethe" at Memory Beta, the wiki for licensed Star Trek works
- "Discovering Vulcan Shame" at MissionLogPodcast.com, a Roddenberry Star Trek podcast
- "Lethe" at Wikipedia
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