From unknown Space, the Tardis returns to Earth, but not to the world Ian and Barbara know. The little blue telephone box has wheeled sharply in the cosmos and cut back through the pattern of history to the struggle between Richard the Lionheart and Saladin, Crusader v. Saracen.

When Barbara is captured by the Saracens and later kidnapped by the monstrous El Akir, Ian appeals to Richard for help, but despite having achieved a splendid victory over Saladin at Arsuf the English King has his own troubles and cannot assist him. So Ian sets out to rescue Barbara alone while the First Doctor becomes involved in court intrigues. In a dramatic climax, Ian finds himself fighting for his life in the harsh, cruel world of the twelfth century, where only the cleverest and strongest survive.