S04E13: 'Journey's End'

The Doctor escapes from regenerating by transferring the energy into his severed hand in the jar, but the Daleks soon transport the Tardis to their Crucible ship. Everyone disembarks apart from Donna, who is inside when the Daleks try to destroy the Tardis. However, the severed hand transfers its energy to her, forming both a human version of Donna with one heart and giving Donna the technical knowledge of a Time Lord, which she will discover later.

Sarah Jane survives extermination when Mickey Smith and Jackie Tyler arrive, with the trio surrendering in order to be taken to the Crucible. Gwen and Ianto at Torchwood are saved when the place becomes time-locked and the Dalek is unable to move. Martha Jones takes the Osterhagen key to a UNIT station in Germany, where she prepares to activate the device which will destroy all life on Earth should the suffering of the human race become too much.

Davros tells The Doctor that the stolen planets will be used in the formation of a 'reality bomb' that will wipe out all forms of life apart from the Daleks. Martha sends a message to the Crucible threatening to destroy the Earth, but The Doctor warns her that the plan is ill advised. Captain Jack is exterminated, but returns to life and meets up with Mickey, Sarah Jane and Jackie.

The countdown to the bomb begins after a short test, but Donna and the human Doctor materialise on the Crucible in the Tardis, much to the shock of everyone on board. The human Doctor is immediately trapped before he can activate an anti-Dalek weapon, but an electrical bolt fired by Davros activates Donna's Time Lord skills. She immediately flicks a few switches and disables the Daleks. It is then revealed that Dalek Caan betrayed the Daleks once he realised their evil disposition.

The human Doctor destroys all the Daleks, disgusting the original Doctor. All the stolen planets are returned to their original location, with the Tardis towing back Earth. The Crucible is destroyed and Davros refuses The Doctor's offer of help.

On Earth, Mickey and Martha head off with Captain Jack after saying farewell to The Doctor and Sarah Jane returns to Luke. The Doctor returns Rose and Jackie to their parallel world and the human Doctor stays with them after sharing a lingering kiss with Rose.

Back on board the Tardis, Donna's mind struggles to cope with the Time Lord factor and The Doctor is forced into wiping her memories of their adventures and meeting in order to save her. He returns her home unconscious and tells Sylvia and Wilf that she must never remember the events. When Donna awakens, she fails to recognise the man who refers to himself as 'John Smith'. After saying goodbye to Wilf, The Doctor returns to the Tardis alone.