Bad Episodes

Riker, Riker

Riker's father, Kyle Riker, arrives on the Enterprise, to be transported to Deep Space Nine for tactical advisement regarding the Marquis and the Cardassians. Along the way, he and Will Riker once again find themselves at odds over things that had happened decades earlier--not only that, but the existence of Thomas Riker only furthers the conflict.

Thomas Riker, serving time in a Cardassian labour camp, hadn't spoken to his father since being found on Nevala IV two years prior. Indeed, Kyle Riker had been unaware of his existence until he'd stolen the Defiant.

However, along the way, the Enterprise finds itself in a strange storm which throws Will and Kyle into the Mirror Universe, where they're forced to put aside their differences to find their way home. In this universe, Thomas Riker is onboard the ship and had assassinated Will for command of the Enterprise, and it seems he's still holding a grudge.

During the final work to get back to the prime universe, Thomas Riker kills Kyle Riker in the transporter room. Will is forced to go back to the prime universe alone--and DS9 doesn't get its strategic advisor, which is considered a blow for Starfleet.