A panicked Picard bursts off the Turbolift in his bathrobe, declaring that he is inexplicably moving back and forth through time. Shaken, he begins to describe the experience to Troi, but is then transported 25 years into the future, working in the vineyard at his home in France. He is visited by Geordi, who has come because Picard is ill with Irumodic Syndrome, an affliction which causes mental deterioration. Picard is then transported to the past, where he is on a shuttlecraft with Tasha Yar, traveling to the U.S.S. Enterprise for the first time. Moments later, he is back in the present, at which point Troi places an urgent call to Sickbay.

Neither Beverly's tests nor Worf's security scans show any indication that Picard physically left the ship. The investigation is then put on hold by news that several Romulan Warbirds are headed for the Neutral Zone, toward a spatial anomaly in the Devron system. Picard is transported back to the future, where he remembers bits and pieces of what just transpired, then tries to explain this to Geordi, who is unconvinced, blaming it on Picard's disease. Geordi is worried enough to take Picard to Cambridge, where Data is a professor. Data decides to explore the possibilities, but Picard is transported back to the past, arriving at the point of his initial arrival on the Enterprise. Among the crew, he sees a group of scraggly humans laughing at him, a sight he has already encountered twice in the future. This is enough for him to suddenly declare a Red Alert.

Since he has foreknowledge of future events, Picard decides not to tell this crew what is happening. He senses a connection when he is told that several vessels are moving toward an anomaly in the Devron system. Starfleet cancels the ship's mission to Farpoint Station, but Picard insists they go there anyway and refuses to explain his decision to the confused crew. Soon afterward, he finds himself back in the present in Beverly's office. She scans Picard, and learns that he has accumulated over two days worth of memories in just a few minutes — real confirmation to what Picard has been saying.

Still in the present, Picard and the crew ponder the significance of the anomaly, which occurred in both the present and the past. Exhausted, Picard lies down in his Ready Room, then finds himself in the future. He insists in going to the Neutral Zone to find the anomaly, causing Geordi to worry about Picard's sanity. Still, he, Data, and Picard ask Riker, who is now an admiral, for help. However, since the Klingons, who have taken over the Romulan Empire, closed their borders to Federation starships, and now control the area, Riker is unwilling to let them proceed. Data proposes they instead travel on a medical ship, and they wind up on a vessel commanded by Beverly, now Picard's ex-wife. Geordi suggests that Worf, who is a governor in the Klingon Empire, might help them enter the territory. Picard then returns to the past, still on course for Farpoint. Suddenly, he finds himself face-to-face with Q, in the courtroom where they first met seven years ago.

Q offers to answer ten "yes" or "no" questions. Picard learns that his time shifting is connected to the "trail" Q put him through seven years earlier, that the spatial anomaly in the Neutral Zone is involved, and that a verdict has been rendered humanity will be destroyed. However, while Q is causing Picard to shift through time, it is Picard, not Q, who is responsible for the imminent destruction. Picard then wakes up in his Ready Room, in the present, and declares a Red Alert...