A man rescued from a derelict ship is not who he says he is.
The Enterprise rescues a wealthy philanthropist, Carter Winston, whose ship was lost, and who is thought to have died. The crew begins to suspect that he is not what he seems, as he behaves strangely and is linked to a Romulan ship. The shape-shifting is revealed as part of a deeper deception.
The story is a mystery involving a being who can take on any form, and a moral question about identity and the right to choose one's own life. Fans remember the surprising twist and the sympathetic treatment of the visitor, who is not a simple villain.