Riker's double steals the Defiant in a plan involving the Maquis.
A man posing as William Riker charms Kira, takes her aboard the Defiant and steals the ship. He is really Thomas Riker, a duplicate made in a transporter accident, who has joined the Maquis, and Sisko joins a Cardassian operation led by Dukat to recover the ship before it sparks a war, watched by an Obsidian Order observer.
Thomas heads for the Orias system, where the Defiant finds a secret Obsidian Order fleet, which the Order is barred from having. Sisko gives Dukat the Defiant's sensor logs of the buildup in return for the ship and crew. Thomas surrenders and is sent to a Cardassian labour camp.