Ruth Clayton

Inside the TARDIS The Doctor’s three travelling companions, Graham O'Brien, Ryan Sinclair and Yasmin Khan, try to get her to talk about her search for The Master (on the assumption that he has managed to escape from the Kasaavin’s realm after the events that took place in "Spyfall"). While doing so The Doctor discovers that The Judoon have descend upon Gloucester, putting the city on lockdown with a forcefield as they search for a fugitive.

Realising that Earth is in great danger, due the brutality of The Judoon, The Doctor manages to bypass the forcefield and they arrive in Gloucester just before The Judoon are about to attack the apartment of Lee and Ruth Clayton, but The Doctor is able to intervene and stall the attack to give her time to question the couple and so discover who The Judoon are searching for.

The Doctor, after getting nowhere questioning the couple, discovers a small alien box in the Claytons' apartment. The Doctor presses them further to tell her the truth, but Lee refuses to answer The Doctor's questions. Lee does however, when time runs out and The Judoon prepare to fire on the apartment, cover the group's escape, turning himself in to The Judoon before being killed by their contractor, Gat, who arrives and recognises him as the fugitive's associate.

A Judoon

At the same time, and unbeknown to The Doctor, Graham has been transported to a stolen spaceship piloted by Captain Jack Harkness, who mistakes Graham for The Doctor. On discovering his mistake, and after they confront The Judoon, Ryan and Yasmin also find themselves being transported to Captain Jack Harkness's spaceship, which is being attacked by those who he stole it from.

Back on Earth, The Doctor and Ruth, on escaping from The Judoon, head for Gloucester Cathedral but are soon surrounded by The Judoon. Out of an uncontrollable instinct, Ruth attacks them, forcing them to retreat after ripping off their commander's horn. With Ruth unable to explain herself, she reveals to The Doctor a text message that Lee sent her before his death. This text message triggers a memory of Ruth's which leads them to a lighthouse where she grew up.

The Judoon Descend Upon Gloucester

When they arrive at the lighthouse The Doctor investigates the surrounding area and discovers the TARDIS buried outside under a blank gravestone. Ruth, meanwhile, has entered the lighthouse and, on breaking a fire alarm box, is engulfed in energy which restores her memory.

The Doctor, confused about finding the TARDIS, is joined by Ruth who introduces herself as ‘The Doctor’. Not realising who The Doctor is Ruth invites The Doctor into her TARDIS. Inside the time-machine The Doctor reveals to Ruth who she is. But this causes more confusion as neither of them remembers being the other, even though The Doctor’s sonic screwdriver identifies them both as being the same person. Ruth explains that she had once worked for Gat, and had hidden from Gat using a Chameleon Arch with Lee as her protector.

Back on Captain Jack Harkness' spaceship, when he learns of The Judoons' force field he deduces that this is what is preventing him from teleporting The Doctor. Captain Jack is forced instead to give her travelling companions a message from the future: to beware of The Lone Cyberman and to not give it what it wants. He is then forced to teleport away due to the spaceship's anti-theft attack system. At the same time Graham, Ryan and Yasmin are transported back to Gloucester.

The Doctor

Meanwhile, The Doctor and Ruth are brought aboard The Judoon’s spaceship where they confront Gat, who is revealed to be a Time Lord with orders to bring Ruth back to Gallifrey, meaning that for them, Gallifrey still exists. This enables The Doctor to deduce that Ruth must be from her past.

Against Ruth's demands, The Doctor reveals her identity – The Judoon scan them both so confirming that they are both the fugitive that they have been looking for. The Doctor then shows Gat a vision of the destroyed Gallifrey she saw. In disbelief and shock, Gat attempts to dismiss this revelation as trickery. Gat shoots at Ruth using a weapon confiscated from Ruth not realising that the gun has been sabotaged and so Gat is killed when the gun backfires.

With Gat killed and The Judoon having lost their client Ruth returns The Doctor to Gloucester and they part ways. The Doctor is then reunited with Graham, Ryan and Yasmin where they relay Captain Jack Harkness' message to her.

Confused by what all the recent events mean - The Master, Captain Jack Harkness, and an incarnation of herself that she can't remember - The Doctor senses that something is coming for her.