The Doctor and the TARDIS are feeling the effects of an anomaly in the Time Vortex. The Doctor hears a familiar tune. Out in the void, there are dozens and dozens of dead spacefish. The Doctor sees a spacecraft that grabs hold of the TARDIS.
The TARDIS is quarantined, and from inside the Doctor tries to make contact. After he has been disinfected, he is allowed to exit his ship while Captain Luisa covers him with a gun. Some spacefish came aboard the ship with the TARDIS, and crewman Cyrus gets too close. He is frozen, all time drained away from him, just like the spacefish.
Oli and the Doctor talk about the Slooks, with Alex's cameras present as usual. The Doctor wants Oli to end the expedition, telling him that he heard the Slook singing in the void.
When Oli is called away to investigate a possible sighting, the Doctor heads to the TARDIS to search for the music that is so familiar. One of Alex's cameras follows him, and he grabs it and reprograms it.
The Doctor shows Oli what the reprogrammed camera recorded: Luisa and Alex conspiring to cathc one of the Slooks. Oli is unsurprised but doesn't want to call off the search.
When the ship finally encounters Slooks, Oli is entranced. The Doctor tries to stop Alex from catching one, but when he fails he heads for the TARDIS. He takes the TARDIS outside the ship to try to scatter the Slooks. They start singing, but the ship harpoons a Slook. It drags the ship, and there are tears in space due to the singing. On board the ship, time slows. Two men in grey take all the recording equipment off the ship, removing any trace of the Slooks.
When the Slooks are gone and their song has ended, time flows again. The two grey men try to take the Doctor's music from him, he retreats to the TARDIS, gloating that even if they take the music from him, it is also in his memory. As he gets away, he realises that they will soon be looking for him.
- The Doctor has a recipe for biscuits from Pliny the Elder.
- The Doctor bought a spinet from George Frederick Handel.