Yesterday's Enterprise - Plot

Plot

The Enterprise-D encounters a rift in space-time while on a routine mission. As they monitor the anomaly, the heavily damaged USS Enterprise-C, a ship believed destroyed more than two decades earlier, emerges. At that occurrence, the Enterprise-D undergoes a sudden and radical change: it is now a warship and the Federation is at war with the Klingons. Worf has disappeared and Tasha Yar mans the tactical station. None of the crew notice the change, but Guinan senses that reality has changed, and has a meeting with Captain Picard. She says, for example, that there are supposed to be children on the ship, leaving Picard greatly surprised. She suggests that the Enterprise-C does not belong in their time and should return to the past. Picard, who knows that this would be a suicide mission, refuses to give such an order on Guinan's intuition alone.

Captain Rachel Garrett of the Enterprise-C and her crew learn they have travelled into the future. Garrett explains that they were responding to a distress call from the Klingon outpost on Narendra III, and were attacked by Romulan warbirds. While the crew works to repair the Enterprise-C and tend to the crew's injuries, Picard and his command staff discuss whether or not the ship should return to the past. Riker argues that their deaths would be meaningless, but Data suggests that it would be considered an honorable act by the Klingons. Picard discusses the situation with Garrett, who tells him that her crew will serve the Federation in the present. Picard quietly reveals to her that the Federation is on the verge of defeat and the presence of one ship will make no difference, but if the Enterprise-C were to return to the past they may prevent the war from ever starting. Garrett agrees and announces to her crew that they will return through the anomaly, but at that moment, the two ships are ambushed by a Klingon Bird of Prey. Garrett is killed, and her helmsman, Richard Castillo, takes command. During the repair efforts, Yar becomes close to Castillo, but is unnerved by tense interactions with Guinan. Guinan reveals to Yar that she knows that Yar dies a meaningless death in the alternate timeline, and the two never should have met. Yar requests a transfer to the Enterprise-C based on Guinan's advice, to which Picard agrees.

As the Enterprise-C prepares to return through the anomaly, three Klingon battlecruisers attack. With the anomaly becoming unstable, Picard orders the Enterprise-D to cover the Enterprise-C's withdrawal. The Enterprise-D suffers major crew losses under the Klingon barrage, including the death of Commander Riker. The Klingons contact the Enterprise-D and demand its surrender. The bridge aflame, Picard defiantly says "That will be the day" before he leaps to the tactical station and manually fires on the Klingons. The Enterprise-C travels back through the anomaly, which causes the timeline to return to normal. Guinan, still subtly aware of the events, asks La Forge to tell her more about Yar.