The Doctor (David Tennant) and Donna (Catherine Tate) visit the planet Midnight, a resort planet though it is bathed in lethal radiation from its star. The Doctor is unable to convince Donna to leave the luxurious spa, so he goes by himself on a shuttle to see a waterfall of sapphires. The shuttle stops unexpectedly, and he joins the driver Joe (Tony Bluto) and the mechanic Claude (Duane Henry) in the cockpit. Everything is functional, but they are not moving. They take a peek through the radiation shielding and Claude thinks something is moving outside. It will take some time before a rescue shuttle will arrive.

Back in the cabin, the Doctor, the Hostess (Rakie Avola) and the other passengers hear knocking on the sides of the shuttle. For a while it seems to be following their movements, but then it stops next to a frightened Sky Silvestry (Lesley Sharp). The shuttle rocks violently and the Hostess goes to check in with Joe and Claude, to find that the cockpit has been ripped away. Sky begins to behave strangely, repeating what the other passengers are saying. Some think she is possessed by whatever is outside, but the Doctor is intrigued.

The delay in Sky’s repetition becomes shorter and Sky is soon speaking in unison with everyone else. Then she says only what the Doctor says. He believes the being outside is trying to learn to speak, to communicate with him. He tries to reason with it. Then Sky starts to speak the Doctor’s words before he does, and the passengers think he’s the one possessed. Sky seems to return to normal but tries to convince the other passengers to throw the Doctor out. They grab him, but the Hostess, hearing Sky use some of the Doctor’s unusual phrases, realizes she is still possessed.

The Hostess grabs Sky and pulls her out into the radiation, killing both of them. The passengers sit silently, shaken and shameful. The Doctor, clearly shaken himself, asks them if anybody knows the Hostess’s name. When the Doctor returns to the spa, he decides to use publicity to force the company to close the planet to tourists.

This was the 200th Doctor Who story. Russell T. Davies wrote it in three days. To arrange Sky’s instant or simultaneous repetition of everyone else’s dialogue was a massive undertaking on the part of the actors and the sound engineers. At one point, they had to recite, rapidly and in sync, the square root of Pi to thirty decimal places. The Doctor’s curiosity, motor-mouth, and air of knowing everything made everyone suspicious of him. He might even have attracted the creature in the first place by raising the radiation shielding. As usual in Old Dark House stories like this, most of the people involved are terribly flawed individuals, even before being taken over by an eldritch abomination. But the characters are beautifully drawn. It was a companion-lite episode as Donna barely appeared; the next episode was doctor-lite because it was all about Donna.

Dee Dee tells the Doctor she has written a paper on the lost moon of Poosh, another in a string of missing planets. Rose appears on a screen for a second when the Doctor’s back is turned. Apparently, the episode was inspired by the Star Trek: The Next Generation episode Darmok. Professor Hobbes was played by David Troughton, son of Second Doctor Patrick Troughton. He has appeared many times on Doctor Who. Director Alice Troughton is not related. Goblin Market, by Christina Rosetti, is quoted: “We must not look at Goblin Men, we must not buy their fruits. Who knows upon what soil they fed their hungry, thirsty roots?” The episode was very well received, described as a tense and claustrophobic psychological drama, creep-show scary, and a nice change-of-pace episode. It was adapted into a stage play.