While traveling to Sarona VIII for shore leave, the U.S.S. Enterprise crew experiences a bizarre phenomenon in which a moment in time mysteriously repeats itself. Shortly thereafter, the ship receives a distress signal from Vandor IV, where Dr. Paul Manheim has been conducting experiments in non-linear time.

After rescuing Dr. Manheim and his wife Jenice, who turns out to be Picard's first love, the crew learns that Manheim's experiment not only caused the time distortion they experienced, but cracked a window into a new dimension. As a result, Manheim's days are numbered, since his neurochemistry has been damaged from floating between two dimensions.

To save Manheim's life and prevent the aborted experiment from ripping into the fabric of the galaxy and confusing everyone's perception of reality, Picard must devise a plan to seal the hole into the other dimension. While Picard tries to resolve his past with Jenice and a jealous Dr. Crusher attempts to come to terms with her feelings for Picard, the away team beams down to Vandor IV to repair Manheim's mistake.

Using Dr. Manheim's lab and his own extraordinary intelligence, Data adds the specific amount of anti-matter necessary to rebalance and align the galaxy. Once the hole is patched, Dr. Manheim's condition improves and Picard is able to resolve his relationship with Jenice once and for all.