David Tennant (The Doctor), Billie Piper (Rose Tyler), and Gabriel Woolf as the voice of the Beast.

The story concludes in the follow-up episode, "".

The crew is assisted by the Ood , a telepathic slave race. However, a mysterious entity known as "The Beast" begins to telepathically possess the Ood, turning them into killers, and eventually possesses the crew member Toby Zed.

This episode marks the first appearance of the Ood, who would go on to become one of the most iconic and complex recurring alien races in the series.

Murray Gold , who crafted the episode's tense, industrial score.