Enterprise meets a version of itself whose crew became stranded in the past, now led by Lorian, the son of Tucker and T'Pol.
Enterprise meets another version of itself, crewed by the descendants of its own crew. In their history, a subspace corridor threw Enterprise more than a century into the past, and the crew lived out their lives there, never stopping the Xindi weapon. The ship's captain is Lorian, the son of Tucker and T'Pol, and an elderly T'Pol is still aboard.
Lorian proposes modifying Enterprise's engines so it can pass through the corridor without being sent back in time, but the two crews clash over how to do it. The episode was directed by Roxann Dawson and written by Mike Sussman.