The Doctor believes he is a human engineer and that Voyager is a hologram.
The Doctor is activated during a red alert to find Voyager almost deserted, and he begins to feel pain and to bleed, which his programming should not allow. A figure claiming to be Reginald Barclay of the Jupiter Station holoprogramming center tells him that he is really his creator, Dr. Lewis Zimmerman, trapped in a malfunctioning simulation of Voyager, and that he must destroy the ship to escape.
Chakotay then appears with the opposite explanation: the Doctor is the ship's hologram, his program is caught in a damaged holodeck, and destroying the ship would erase him. The Doctor chooses to believe he is a hologram and is safely recovered. The episode brought Dwight Schultz's Barclay, a Next Generation character, to Voyager.