What does Finnian Valentine know? And can Leela and the Master ever truly be on the same side?
Narvin informs Romana that the Master is waiting in solitary confinement and that the war has given him purpose and changed him for the worse. With the Doctor refusing to help, Romana ignores Narvin's warnings and says that they need somebody intelligent, ruthless and, if necessary, to serve as a scapegoat. The pair meet with him in the cells.
With assault forces breaching the atmosphere, Finnian Valentine arms and activates an explosive weapon, expecting to die. Instead, he has conflicting memories about if he knew his parents, if he married a man or a woman and if some people that he knew were killed by the Daleks or the Time Lords. He wakes up, confused.
Romana and Narvin offer the Master a pardon in return for his help in recovering Valentine, a Barvan freedom fighter whose last known location was in the Blayling system where he and his allies were hoping to free slaves on Konoi VII, including his husband. The Master declines the invitation until Romana offers him the freedom of time and space with no questions asked; he insists on having his TARDIS, which Romana agrees to so long as Leela joins him on the mission.
Tasked with getting information on a possible weapon from Valentine, Leela and the Master depart for Konoi VII. Leela tells him that she does not like his new body as his decayed form did not disguise his hate as this one does. After a bumpy ride, they arrive and go into the trenches, Leela aware that somebody is watching them. They find Valentine tied up in a bunker and are joined by the person who has been watching them: a second Valentine. The Master deduces that a temporal weapon killed Valentine and left two very different iterations behind in his place as the timelines were shattered around him.
Neither Valentine wants to go with Leela and the Master, so the Master stuns them with his laser screwdriver so that they can be interrogated. Leela and the Master take one each; whilst the one with Leela blames the Time Lords for the deaths of his parents, sister and lover, the one with the Master is grateful to the Time Lords for saving his planet from the Daleks. The Master asks his version about the weapon and tries to hypnotise him into trusting and obeying him. Leela's calls her a politician who uses words instead of action and spits at her after calling her pathetic.
The Master's hypnosis makes his Valentine remember the detonation. He goes to see Leela after hearing a struggle between her and her Valentine and takes her knife from her, going with her to talk in private. Leela has learnt nothing and the Master's hypnosis will not work due to the Valentines' minds being too far gone. They swap Valentines and both claim that they have had no success, making the Master realise that they should be interrogating them together so that their reaction to one another can be observed. They identify one as the weaker and the Master points a gun at him, learning that the weapon is called the Possibility Cannon and is in the Isop Galaxy and that part of it was entrusted to Valentine. That part was used to cause the explosion.
The Master kills the weaker one, believing that he was lying as somebody so committed to their cause would not reveal the truth so easily. Leela is angry with him and refuses to allow him to kill the remaining Valentine. He gives Valentine 45 seconds to tell the truth before killing him; he says that the weapon is actually a power source which was on Arcking before it was destroyed by the Daleks and time locked. The Master believes that he is mostly telling the truth and uses his screwdriver to cause him temporal decomposition, forcing him to live his entire life cycle in twenty minutes. Noticing Leela's micro-expressions, the Master knows that Valentine had already told Leela about Arcking and had no intention to tell him.
Leela and the Master return to the TARDIS. The Master denies that he will be wiping Leela's mind to keep her from telling Romana about Arcking and instead straps himself in and opens the doors mid-flight. As she struggles to keep herself from falling into the Time Vortex, the Master reveals that the Time Lords are incapable of recalling him to Gallifrey and that he had come willingly in the hopes of gaining information. She falls from the TARDIS into the Vortex and screams. The Master sets the coordinates for Arcking.
Romana and Narvin have no news from Leela or the Master and are unable to track the TARDIS. Romana regrets that they sent Leela with him on her own, but Narvin reminds her that he disagreed with the plan.
- Romana - Lalla Ward
- Leela - Louise Jameson
- Narvin - Seán Carlsen
- The Master - Derek Jacobi
- Finnian Valentine - Bryan Dick
- Finnian is a Barvan freedom fighter.
- Konoi VII is in the Blayling system.
- One Valentine says that the Time Lords killed his parents and sister.
- One Valentine claims that the Possibility Cannon is located in the Isop Galaxy.
- The Devil You Know was recorded on 23 April 2017, the day before recording for Only the Good began.
- The scene from this story where the Master betrays Leela was illustrated by Jamie Lenman for The DWM Review in DWM 524.
- Romana refers to Narvin resurrecting the Master for such an eventuality as the Time War. (AUDIO: Eyes of the Master, The Death of Hope)
- The Master says that he only retrieved his TARDIS recently. (AUDIO: Beneath the Viscoid)
- Leela refers to meeting the Master in his "husk" form. (AUDIO: Trail of the White Worm)
- Valentine's information leads the Master to Arcking. (AUDIO: The Good Master)
- The Master uses his TARDIS' straps. The Sixth Doctor and Peri Brown used the straps in the Doctor's TARDIS in Timelash.