Planet of the Dead

The episode begins with a young thrill-seeking burglar, Lady Christina de Souza stealing a gold chalice once belonging to King Athelstan from a museum. She then narrowly evades the police by riding on a London bus on which the Doctor is also travelling, shortly before the bus suddenly passes through a wormhole and arrives on the desert planet of San Helios. The Doctor and the other passengers find that while the wormhole is still present, returning on foot is not possible, after the bus driver is killed trying to cross back, evaporating to a skeleton instantly; the passengers deduce that the bus had protected them like a Faraday cage. Seeing the driver's skeleton coming out on the other side of the portal, the police call in UNIT, commanded by Captain Erisa Magambo and aided by scientific adviser Malcolm Taylor, to close the wormhole.
Trapped on the heavily damaged bus, the other passengers introduce themselves: Angela is a middle-aged mother travelling home to her family; Lou and Carmen are an elderly couple who win £10 each time they play the National Lottery due to Carmen's low-level psychic abilities; also Barclay, who was travelling to a friend's house to ask her on a date; and Nathan, who was travelling home to watch television. The Doctor and Christina decide to scout the planet, spotting an approaching storm, while Nathan and Barclay try to fix the bus. As they travel, the Doctor learns of Christina's troubled history, and appreciates her callousness and aptitude in their alien situation. The Doctor and Christina encounter the Tritovores, an anthropomorphic fly species, who take them to their wrecked spaceship.
After clearing up a misunderstanding, the Tritovores explain that they were making a routine goods collection with San Helios before they crashed, revealing the planet to had housed a hundred billion inhabitants and a thriving ecosystem. The Tritovores send out a probe to investigate the cause, and discover a large swarm of metallic stingray-like aliens who routinely create wormholes and destroy ecospheres as their biological imperative. To rescue the Tritovores and the bus passengers, Christina uses her burglary skills to retrieve a crystal which powers the spaceship (together with the pedestal it is located on), unintentionally awakening the stingrays that were inactive within the ship, one of which devours the two Tritovores. The Doctor attaches parts of the pedestal to the bus and uses the chalice of Athelstan as an interface to the technology (much to Christina's fury). This allows the bus to fly through the wormhole, with the stingrays in hot pursuit. Taylor quickly closes the wormhole but not before three of the stingrays pass through it. After UNIT shoots down the stingrays and the passengers have been debriefed, Christina offers to the Doctor to let her travel with him, but he coldly rejects her because he has no wish to lose another companion.
The characters part ways again. The Doctor recommends that UNIT hire Barclay and Nathan, Christina is arrested by the police for the theft and Carmen has a premonition that visibly unnerves the Doctor:
You be careful, because your song is ending, sir. It is returning, it is returning through the dark. And then Doctor... oh, but then...he will knock four times.As a final act of kindness, the Doctor uses his sonic screwdriver to release Christina from her handcuffs, allowing her to escape. The pair part on good terms as she flies away in the bus and the Doctor enters his TARDIS and dematerialises.