Rose requests a trip back to the day her father, Pete Tyler, died. Reluctantly, the Doctor agrees, but he realises he has made a mistake, when Rose saves Pete from being run over by a car. This has now changed the timeline, and Reapers are transposing themselves all over the Universe. However, this time, the Doctor doesn't have a plan…

After the TARDIS makes a crash landing on the Earth of another universe, Rose discovers her father is alive and rich, Mickey encounters his alternative self, and the Tenth Doctor learns one of his oldest and deadliest foes is about to be reborn.

The plans of John Lumic to convert the world into Cybermen are now in full force. The Tenth Doctor, Rose, Mickey and the Preachers must find a way to stop him from enforcing his "ultimate upgrade."

Humanity is caught in the crossfire as the Cybermen and the Daleks wage war against each other. When the mysterious Genesis Ark opens, the Tenth Doctor is faced with an impossible decision: saving the world could mean losing Rose Tyler forever…