Picard and the Enterprise crew are sent to investigate what appears to be the defection of Ambassador Spock to Romulus. Captain Picard and Lt. Cmdr. Data disguise themselves as Romulans and are transported to Romulus. There they discover that Spock is actually attempting the reunification of Vulcan and Romulus, and working with a Romulan underground movement. Picard's Romulan nemesis, Command Sela, reappears and captures the Starfleet officers and the ambassador, all as part of a plan to conquer Vulcan. The three must escape from their Romulan prison and foil the Sela's plans for invasion.