The Enterpriseis in orbit around the planer Bre'el IV, trying to help prevent an asteroidal moon from falling onto the planet, which would cause worldwide devastation. In the middle of an attempt to prevent this, a naked Q appears on the bridge.
Q has been stripped of his powers and banished from the Continuum for misbehavior. The Enterprise crew is not sure whether to either believe or trust him, but his obvious discomfort at dealing with being mortal – feeling hunger and pain, emotions, retaining his vast knowledge but unable to use it – seems to cause a reluctant change of heart. Since he retains his arrogant personality, Q still finds it difficult to fit in. He is also suspected of being the cause of the falling asteroid's instability.
His powerlessness is made manifest when the Calamarian, a race of creatures with a collective consciousness, attacks him with injurious results. Making matters worse, the Enterprise is in danger as long as he is on board, hindering their efforts to help the Bre'el.
Eventually, Q decides that being human is too much for him to deal with, and he steals a shuttle to draw the Calamarian away from the Enterprise, even though in his mortal form he will surely be killed. Enter Q2, who has been keeping an eye on the situation on behalf of the Continuum. As a reward for an unheard-of (for Q) act of self-sacrifice, Q's powers are restored, but his impulse to avenge himself on the Calamarian demonstrates that he is still on probation.
Since the Enterprise crew helped him redeem himself, Q decides to reward the crew. The moon is restored to its orbit, with Enterprise getting the credit, but his other rewards are not received as well, except by Data, who is given a chance to laugh.