The Battle in the Bassen Rift was a conflict fought in 2379 between the Sovereign-class USS Enterprise-E, assisted by two Valdore-type warbirds of the Romulan Star Empire, against the Reman warbird Scimitar, a unique and heavily armed spacecraft commanded by Shinzon.
Shinzon was a clone of Starfleet Captain Jean-Luc Picard, the Enterprise's commanding officer, and had developed a vendetta against his originator. The resultant battle was a fierce engagement which ended with the defeat of the Scimitar, only thanks to sabotage from within the Reman starship itself, and left the Enterprise and the pair of warbirds severely damaged. (Star Trek Nemesis)
Shinzon, allied with the Remans, led a coup against the Romulans, assassinating most of the Romulan Senate and assuming the role of Praetor himself. Soon thereafter, Shinzon made overtures to the Federation, requesting that an envoy be sent for face-to-face meetings on Romulus, ostensibly to establish peace with the Romulans.
Admiral Kathryn Janeway sent the Enterprise-E on the mission, as it was the closest available starship. However, Starfleet did not learn until later that Shinzon had secretly arranged for the Enterprise to be the starship that would be sent, by placing a lure for the Enterprise crew, in the form of the Soong-type android B-4 on Kolarus III.
Shinzon specifically wanted to divert Picard to Romulus, because he required a complete transfusion of Picard's blood in order to survive. Because his temporal RNA sequences had not been activated, his cellular structure was slowly breaking down. Shinzon also wanted to learn more about his counterpart and their "shared" identity.
However, the crew of the Enterprise-E soon managed to see through Shinzon's deceptions. They determined that the Scimitar was equipped with a thalaron radiation generator, a type of biogenic weapon that could effectively destroy all life on a starship or an entire planet in a matter of moments. Although Shinzon managed to capture Picard via transporter, Picard quickly escaped with the assistance of Data, who had masqueraded as B-4. Once Picard and Data were safely aboard, the Enterprise departed Romulus at maximum warp.
The Scimitar pursued the Enterprise while cloaked, waiting for the right moment to strike. Shinzon himself continued to deteriorate both physically and mentally. On the Enterprise, Picard and his senior staff realized that the Scimitar had to be destroyed, lest it continue to threaten the Federation with its massive weaponry and its planet-destroying thalaron weapon.
Fortunately, they also realized that Shinzon needed Picard's blood quickly, or he would die due to his unstable genetic structure (Shinzon had been created with the intention that he would be rapidly aged at a certain point to match Picard, but he had never received such a "signal" and his body was thus breaking down), meaning that Shinzon would be forced to attack the Enterprise before launching any other campaign.
The Enterprise was ordered to rendezvous with Star Fleet Battle Group Omega near the Bassen Rift, where it would have the support of other starships. However, Shinzon had been planning ahead – when the Enterprise's subspace communications with Starfleet were disrupted by the rift, the Scimitar quickly launched its attack. Firing while still cloaked, the Scimitar quickly disabled the Enterprise's warp drive with a single volley and left it stranded, outgunned and unable to call for help.
Although the Scimitar remained cloaked, the Enterprise was able to briefly locate and land some hits on the Scimitar by firing all the Sovereign-class starship's phaser banks at a zero degree elevation, scanning for shield impacts to attempt torpedo strikes, although the Scimitar was too fast for the Enterprise to reliably land hits. The Enterprise's retaliation inflicted minimal damage to Shinzon's starship while the Scimitar was able to weaken the Enterprise's dorsal shields.
A brief ceasefire ensued where Shinzon projected a hologram of himself into the captain's ready room, where he offered Picard the chance to give himself up so that nobody else on the Enterprise would have to die. Picard refused, and the battle was set to resume. As it looked as though hope had all but disappeared, two Romulan Valdore-type warbirds decloaked between the two starships.
Commander William T. Riker initially feared that these starships were more hostiles, but his anxieties were relieved when Commander Donatra, CO of the Valdore, hailed the Enterprise, informing Picard that the Empire considered Shinzon's attacks a matter of "internal security" and offered to assist in destroying the Scimitar. While triangulating fire between their three starships, the warbirds and the Enterprise were able to score several direct hits on the Reman warship before the Scimitar's superior firepower disabled the warbirds.
On the Enterprise bridge, ship's counselor Deanna Troi offered a means of tracking the Scimitar through its cloaking device – by telepathically contacting the Reman Reman Viceroy (who had previously contacted Troi in the same way), triangulating his position and disabling the starship's cloaking device.
With several quadrants of the Enterprise's deflector shields failing, Shinzon then ordered that a boarding party be beamed aboard the Enterprise to bring him Picard. However, the Reman troops were quickly pinned down by Enterprise security personnel on Deck 29. The viceroy, who was leading the boarding party, was ultimately killed in the assault by Commander Riker.
During the battle on Deck 29, the Scimitar fired a spread of photon torpedoes at the Enterprise, destroying the front of the Federation flagship's bridge, causing an explosive decompression, which killed Lieutenant Branson before an emergency force field was erected to seal the hull breach.
With the battle deteriorating into one of sheer attrition, it appeared that the Scimitar would win thanks to its superior weaponry and shielding – the Enterprise had depleted its complement of photon torpedoes, and phasers were only operating at four percent, while the Scimitar's shields were still running at seventy percent.
However, Picard wryly commented that, in his youth, his first evaluation at Starfleet Academy had suggested that he was extremely overconfident – a trait he attributed to Shinzon as well. In order to stop the Scimitar, Picard ordered the Enterprise to ram the enemy starship at full impulse when Shinzon moved the Scimitar into position in front of the Enterprise so that he could look directly at Picard when ordering his surrender, plowing the two opponents together.
Although the Enterprise sustained critical damage in the ramming maneuver, the Scimitar remained primarily operational, though the starship's disruptors were disabled. Picard tried to sacrifice the Enterprise by activating the auto-destruct sequence, but it was off-line due to heavy damage. In a final act of desperation, Shinzon ordered the activation of the thalaron radiation weapon, and ordered that every living thing on the Enterprise be killed.
Picard ordered Lieutenant Commander Geordi La Forge to beam him aboard the Scimitar so Picard could stop the weapon from firing. Just after transport, however, the transporters malfunctioned, making it impossible to bring the captain back. Data decided to launch a daring rescue mission (being unaffected by the vacuum of space), hurling himself across the gap between the two starships to board the Scimitar as well.
On the Scimitar, Picard battled his way through the bridge, before he and Shinzon engaged in a final confrontation in the thalaron generator room as the seconds counted down towards the firing of the thalaron weapon. Picard managed to kill Shinzon in hand-to-hand combat with barely thirty seconds remaining in the countdown.
At this point, Data arrived on the bridge and beamed Picard away using an emergency transport unit, and firing on the thalaron radiation generator with his phaser, destroying the Scimitar and sacrificing himself to save the eight hundred men and women aboard the Enterprise.
The battle ultimately brought about a greater understanding between the Federation and the Romulans, as the two former enemies had fought side by side in battle. The valor with which the Enterprise fought against Shinzon greatly impressed the Romulans, and the Romulans' decision to assist the Enterprise also impressed Starfleet.
Following the battle, newly-promoted Captain William T. Riker of the USS Titan led a Starfleet task force to the Romulan border to engage in preliminary talks for a peace accord between the two sides. It was hoped that this development would lead to greater understanding and a new era of peace in the Alpha and Beta Quadrants. (Star Trek Nemesis)
Star Trek Nemesis screenwriter John Logan wanted this battle to be fought with a fleet of ships, instead of just the four vessels that fight in the final version. However, having the battle incorporate a fleet proved too costly. (Star Trek: The Official Starships Collection, issue 31, p. 9)
In the first draft script of Star Trek Nemesis, this conflict took place "over Earth" (repeatedly phrased that way in the script's stage directions).
Star Trek Online's description of the Bassen Rift (called in-game by its Romulan name, "Great Bloom") states that, even thirty years after the battle, the area continues to be irradiated with traces of thalaron radiation left over from the Scimitar's destruction.