The crew confronts aliens who feed on humans in nineteenth-century San Francisco.
The Enterprise officers are stranded in nineteenth-century San Francisco, trying to blend in while they search for a way to stop alien beings who are feeding on human life energy. They meet the writer Mark Twain, who becomes an important ally and an unexpected passenger in the effort. The crew has to use a combination of ingenuity and luck.
The story is a lighthearted time-travel romp with a serious edge, and the climax involves a risky plan to return to the future. Data's fate is at the heart of the story, and the conclusion is both a sacrifice and a sign of friendship. The episode is a fun start to the sixth season, with a clever use of its historical setting.