Planet of the Dead

The episode depicts Christina fleeing the police from a museum robbery by boarding a bus that accidentally travels from London to the desert planet of San Helios, trapping her, the Doctor, and several passengers on board the damaged vehicle. After the bus driver dies trying to return to Earth, the Unified Intelligence Taskforce, headed by Captain Erisa Magambo (Noma Dumezweni) and scientific advisor Malcolm Taylor (Lee Evans), attempt to return the bus while preventing a race of metallic stingray aliens from posing a threat to Earth. At the end of the episode, one of the passengers delivers a warning to the Doctor that "he will knock four times", foreshadowing the remaining three specials.