Defiant

A visitor who appears to be Commander William Riker charms Kira into giving him a tour of the Defiant, then stuns her and steals the ship. He is really Thomas Riker, the transporter duplicate left stranded for eight years, who has joined the Maquis partly to step out of his more successful twin's shadow. He takes the cloaked ship into Cardassian space to expose a suspected military build-up in the Orias system. With war a real risk, Sisko works alongside Dukat on Cardassia to track the Defiant, while Kira quietly sabotages it. The Orias ships turn out to belong to the Obsidian Order, which is forbidden its own fleet, and Sisko uses this to strike a deal: the Defiant and its crew go home, in return for the ship's sensor logs. Thomas surrenders, facing a Cardassian labour camp rather than execution, and Kira promises to get him out one day.