Star Trek: 25 Greatest Next Generation Episodes

In what is the closest thing to a mirror universe episode in TNG, the Enterprise-C, destroyed over 20 years ago, is found adrift in a time displacement causing history to be dramatically altered. No Worf, no Troi, Tasha is alive and the Enterprise is a hardened battle cruiser. The presumed retreat by the Enterprise-C during a rescue mission at a Klingon outpost results in twenty years of war between the Federation and the Klingons.

The Enterprise survivors adjust to life in the future and the consequences of their actions while debating whether or not to return to battle, certain to be destroyed, but before they can, Captain Garrett of the Enterprise-C is killed in a surprise Klingon attack, meaning history cannot possibly be fully restored.

Tasha returns with the Enterprise-C manning tactical, the tactical officer Lt. Castillo returning as Captain, and in the midst of a massive firefight resulting in the Enterprise-D's destruction, the Enterprise-C withdraws into the time displacement, the timeline seemingly restored and the crew of the undamaged, normal universe Enterprise-D with no memory of the events that transpired. The events in the displaced timeline, however, will have long lasting effects throughout the rest of the series.

Now, on to the winner...