The governor of Krios, Vagh, accused the Federation of providing aid and weapons to Kriosian rebels who were seeking independence from the Klingon Empire. In 2367, Kell came aboard the USS Enterprise-D, which had been dispatched to meet with Vagh to disprove accusations that the Federation was secretly supplying phasers and other material support to the rebels. Kell accompanied the Enterprise-D on this mission. Vagh ordered the Enterprise-D not to leave orbit or it would be attacked. Ambassador Kell offered to beam down to Krios to force Vagh to come aboard the Enterprise-D to witness the ongoing investigation, in an attempt to convince him of the Federation's innocence.
It was during this mission that Geordi La Forge was abducted and "brainwashed" by the Romulans for the purpose of murdering Vagh, further implicating the Federation in the Kriosian rebellion. Vagh's death would have all but certainly caused a new war between the Federation and the Klingons, something that had been a major strategic aim of the Romulan Empire for many years.
Before Kell left, La Forge visited him in his quarters. Kell, who was conspiring with the Romulans, had implanted commands from the Romulan commander Sela within La Forge's mind. Kell ordered him to transport the weapons to the Klingon rebels and for La Forge to murder Governor Vagh when he arrived from Krios and claim he acted on behalf of Starfleet in support of the colony's independence. Data was able to foil the plot by finding evidence of Romulan energy sources in the weapons and La Forge's VISOR. Data was able to trace the signal to Kell.
Kell was arrested but refused to be searched by the crew of the Enterprise-D, stating that he was a representative of the Klingon High Council. Vagh agreed with Kell, and said that the Klingons would search him. Kell was remanded into the custody of Vagh. Kell knew this was a death sentence and requested asylum aboard the Enterprise-D, but Captain Jean-Luc Picard said that he would grant asylum only after Kell was absolved of the crime of which he was accused. (TNG: "The Mind's Eye")