The Doctor assumes the guise of the crew.
Aliens from the Hierarchy abduct Janeway and demand that Voyager hand over its warp core. Threatened with her death if he tells anyone, the Doctor uses his holo-emitter to impersonate several crew members in turn, including Chakotay, Torres and Janeway herself, as he tries to meet their demands.
The deception eventually unravels, and the crew works with the Doctor to rescue Janeway and defeat the Hierarchy. Believing he is about to be deactivated, the Doctor confesses a string of secrets to his crewmates, which leaves him embarrassed once he survives. It was the last episode before the two-part finale.