Set in the 24th century, the series follows the adventures on Deep Space Nine, a space station located near a stable wormhole between the Alpha and Gamma quadrants of the Milky Way Galaxy. In this episode, a telepathic attack on Dr. Julian Bashir (Alexander Siddig) causes him to experience rapid ageing as the station suffers a strange power failure and his crewmates begin acting strangely.
A strange alien named Altovar (Victor Rivers) zaps Dr. Bashir with an electrical field, knocking him unconscious. When he awakens, he finds that he has begun to age quickly. Furthermore, the station is dark and deserted, apparently having undergone some catastrophe.
Bashir explores the silent station and walks in on several members of the crew arguing. They barely notice him when he walks in, and seem unfazed by his graying hair and wrinkling skin. Barely audible whispers echo in the background, and when Chief O'Brien (Colm Meaney) begins repairing the communications system, Bashir hears that the whispers are actually the voices of his crewmates, and they are talking about him. They say he is in a coma, and he is dying.
Bashir realizes that the crew and the empty station are all in his head, and he is actually living in a dreamlike state within his comatose mind. The alien Altovar appears. He grabs Lt. Dax (Terry Farrell) and drags her away. Bashir feels that he has lost something, and realizes that each member of the crew in this vision represents part of himself. When the alien captures Commander Sisko (Avery Brooks), it is as though he has taken away the most steady, able part of his personality, crippling him. The alien threatens to kill each crew member, chipping away at Bashir's psyche until there is nothing left.
Bashir ages quickly, reaching a weakened, elderly state. He and Garak (Andrew J. Robinson) go to Ops, where the last of the crew lie dying. Garak prods Bashir, trying to convince him to just give up and die, but Bashir works hard with the last of his strength to find out what is going on. Garak becomes more insistent, and Bashir figures out that he is actually Altovar. Knowing this, he can shrug off Garak's taunting and make his way back to the Infirmary, his home base on the station. This gives him more strength and he uses it to trap and kill Altovar. He awakens from his coma, with his real crewmates keeping vigil over him.
Afterward, while Bashir is eating lunch with Garak, he appears hurt that Bashir's mind would present him (Garak) as Altovar. He quickly adds with a bit of admiration that there is still hope for Bashir.