This episode launched the longest-running science fiction series in history. It established core elements that remain today, from the blue police box exterior to the concept of the Doctor traveling with human companions.

: Unlike the heroic figure of later years, the First Doctor is initially abrasive and suspicious, even kidnapping Ian and Barbara to protect his secrets.

The story begins at Coal Hill School in London, where two teachers, Ian Chesterton and Barbara Wright, become intrigued by their unusual student, . Her advanced knowledge of science and history—combined with her strange gaps in everyday 1963 knowledge—leads them to follow her home.