The Doctor and Donna land in London. They're worried about weaknesses in parallel worlds and go back to the Tardis. While they are inside the Earth disappears.
Jack Harkness, Martha Jones, and Sarah Jane Smith are all on Earth, as well as Donna's parents. Rose Tyler appears on Earth as well with a large weapon. They all look up in the sky to see that all of the stars are gone, replaced by 26 other planets very close by.
Spaceships head towards Earth. They are Daleks, who land and begin taking over the planet.
The Doctor goes to the Shadow Proclamation where they meet a lady who tells them that 24 worlds have disappeared from the sky. The Doctor realizes planets are being taken from time as well as space, and they have fallen into a formation where they all revolve around each other.
Martha is informed that Project Indigo has been activated, despite its experimental status. It is a teleportation device. Harkness urges her not to try the untested technology, but Jones activates the device. Harkness thinks she has been scattered into atoms.
Donna points out that bees have been disappearing, and from this the Doctor extrapolates the location of the Earth. The Lady wants the Doctor to declare war and lead them into battle, but his nonviolent principles forbid this, and he and Donna leave in the Tardis. They follow the Earth's trail to the Medusa Cascade, but can trace it no further.
Donna's parents try to escape and are saved when Rose blasts a Dalek with her gun. Rose explains that she is trying to trace the Doctor through Donna and her parents. Their computer turns itself on; an incoming message is transmitted from Harriet Jones and she starts a Google Hangout with all of the companions. Rose can overhear but cannot communicate. Martha survived and was teleported to her home. Harriet Jones wants all people who might be able to track the Doctor to team up to find him. They come up with a plan to boost the signal of Martha's cellphone in hopes of establishing communication, although the signal will then be visible to the Daleks.
The signal reaches the Doctor and he attempts to follow it back to the Earth, while the Daleks break in to Harriet Jones's home and she disappears from the Hangout, after transferring control of the signal to Torchwood.
The Doctor joins the Hangout. Rose is disappointed that the Doctor can't see her. The Daleks manage to cut the signal and the Dalek leader talks to the Doctor. He's created a new race of Daleks using cells from his own body.
The Daleks decide to destroy all of the companions, starting with Torchwood. Harkness, Sarah Jane, and Rose all set out to find the Doctor, but a Dalek sends a beam through the doctor, fatally wounding him. The companions drag him to the Tardis, where he performs a regeneration.