Doctor: David Tennant (Tenth Doctor)
Companions: Freema Agyeman (Martha Jones)
John Barrowman (Jack Harkness)
John Simm – The Master
Alexandra Moen – Lucy Saxon
Adjoa Andoh – Francine Jones
Trevor Laird – Clive Jones
Gugu Mbatha-Raw – Tish Jones
Reggie Yates – Leo Jones
Tom Ellis – Thomas Milligan
Ellie Haddington – Professor Docherty
Tom Golding – Lad
Natasha Alexander – Woman
Zoe Thorne, Gerard Logan, and Johnnie Lyne-Pirkis – Toclafane voices
Directed by Colin Teague
Written by Russell T Davies
Script editor Simon Winstone
Produced by Phil Collinson
Executive producer(s) Russell T Davies
Incidental music composer Murray Gold
Production code 3.13
Series Series 3
Length 3rd of 3-part story, 52 minutes
Originally broadcast 30 June 2007
A year after the appearance of the Toclafane on Earth, humanity is on the verge of extinction. After her escape from the Valiant, Martha has been travelling around the world and avoiding the Master's detection through the use of her perception filter. She has been contacting groups of people to find a special gun created by Torchwood and UNIT that can kill the Master. Martha meets Thomas Milligan, a former doctor who leads her to Professor Docherty. Together they manage to capture a Toclafane. Upon examination they discover the Toclafane are the humans from the far future who took the rocket to Utopia. They were driven insane after discovering that Utopia was a lie. The Master created the Paradox Machine to allow them to return to the past and kill their ancestors while avoiding the grandfather paradox. Martha and Thomas leave to find the last component of the gun, and Docherty provides the Master with Martha's location in exchange for information on her own son.
The Master's forces corner Martha and Thomas, and Martha surrenders but Thomas rushes the Master in a rage and is shot. The Master destroys the gun Martha assembled and takes her back to the Valiant so he can kill her in front of the artificially aged Doctor. The Master readies the launch of the Toclafane fleets to conquer the rest of the universe and demands Martha kneel before him. The Master basks in the glory of the last few moments of the countdown and Martha begins to smile. She reveals that the gun was simply a distraction from the real plan, she had really spent the last year following the Doctor's instructions. Martha has been preparing the surviving humans to concentrate their thoughts on the Doctor upon the completion of the launch countdown. The Doctor has spent the past year psychically integrating himself into the Master's Archangel network, which channels the collective psychic energy of the people to the Doctor. A rejuvenated Doctor overcomes his captivity and forces the Master to cower in defeat.
Martha and her family free Jack Harkness and set off to destroy the Paradox Machine while the Master tries to detonate the fleet. The Doctor persuades the Master to stop, and the Paradox Machine is destroyed. Time snaps back, and the events of the last year are erased and the Toclafane disappear. Aboard the Valiant, everyone can still remember what happened because they were at the centre of the events. The Doctor and his allies consider the Master's fate before the Master is shot by his wife Lucy. The Master refuses to regenerate for the Doctor and dies in his arms, leaving the Doctor to believe he is the last Time Lord. The Doctor cremates the Master's body on a funeral pyre and leaves, but sometime later a woman's hand picks up the Master's signet ring from the ashes.
The Doctor returns Jack to Torchwood, while Martha decides to leave the Doctor to care for her family and finish medical school. She gives him her mobile phone in case she needs to contact him, saying that if it rings he must come right away. The Doctor pilots the TARDIS away and contemplates events when the bow of a ship called the Titanic bursts through a wall of the control room, leaving the Doctor confused.