The episode serves to provide character development of CaptainJean-Luc Picard, who is featured in this episode to the general exclusion of the rest of the cast. Its primary theme, explored in many other stories (starting with H. G. Wells' The Time Machine), is the effect on the present of changing the past. However, the primary literary theme is the balance of order and chaos within the individual.
When Captain Picard and an away team are attacked by a group of radicals, an energy blast damages his artificial heart. Picard finds himself in the afterlife, which appears to be the domain of Q, who bluntly says, "Welcome to the afterlife, Jean-Luc. You're dead."
To prove Picard is dead, Q introduces him to people that Picard knows have died, including his father and the voices of people for whose deaths Picard is responsible. When Picard accuses Q of causing his death, Q reveals that Picard's artificial heart caused his demise: a natural heart would have endured the energy blast he suffered.
Picard's original heart was damaged during a bar brawl with Nausicaans - a quick-tempered, bullish race, one of whom stabbed him through the heart. Picard realizes his regret for his "wild youth" and that it has caught up with him. His current disciplined personality and seriousness is rooted in regret over his earlier lifestyle.
Q offers to let Picard go back in time to prevent himself from being stabbed. Q assures him that any changes he makes will not affect anyone other than himself. He is sent back to two days before the injury, meeting with friends and academy classmates Corey Zweller and Marta Batanides. His "newly changed" personality comes as somewhat of an unpleasant surprise, and he alienates his friends - the person they knew as fun loving and quick to anger is now staid, slow to anger, and often unintentionally insulting.
Events proceed as they did with Zweller becoming enraged with a group of Nausicaans who cheat him at dom-jot. Picard blocks Zweller's plan to cheat them back by rigging the dom-jot table, angering his best friend. The next day the Nausicaans taunt Picard and his friends. Instead of taking on the Nausicaans, Picard throws Zweller out of the way of the fight. The Nausicaans call them cowards, and leave - as do Zweller and Batanides. Picard has destroyed his friendship with them by refusing to stand up for Zweller. Q tells Picard that he saved his heart, and returns him to the present.
Picard finds himself on the Enterprise as a Lieutenant junior grade in the astrophysics department. Q tells him that, as a consequence of the changes to his past, he has led an unremarkable career doing routine work. Picard consults with Riker and Troi on the possibility of him moving on to higher positions; while they consider Picard a competent and hardworking officer, he fails to show initiative and does not take the necessary risks to have a successful command career in Starfleet.
Picard confronts Q, who tells him that although the bout with the Nausicaan nearly cost him his life, it also gave him a sense of his mortality. It taught him that life was too precious to squander by playing it safe. Picard realizes that his attempts to suppress and ignore the consequences of his indiscretions have resulted in him losing a part of himself. Picard then declares that he would rather die as captain of the Enterprise than live as a nobody. Q sends him back to the bar fight and events unfold as they did originally, with Picard being stabbed through the heart and laughing as he collapses to the floor. In the present, Captain Picard awakens, having been revived by Dr. Crusher.
As Picard recovers from his injuries, he wonders whether he really journeyed into the past or whether it was merely a hallucination or one of Q's tricks. Riker expresses some difficulty imagining Picard taking on three Nausicaans. As the episode ends, Picard launches into another story about a prior encounter with Nausicaans.