Doctor: Peter Capaldi (Twelfth Doctor)
Companion: Jenna Coleman (Clara Oswald)
Colin McFarlane – Moran
Sophie Stone – Cass
Zaqi Ismail – Lunn
Morven Christie – O'Donnell
Arsher Ali – Bennett
Steven Robertson – Pritchard
Paul Kaye – Prentis
Neil Fingleton – The Fisher King
Peter Serafinowicz – Voice of the Fisher King
Corey Taylor – Roar of the Fisher King
Directed by Daniel O'Hara
Written by Toby Whithouse
Script editor Nick Lambon
Produced by Derek Ritchie
Executive producer(s) Steven Moffat
Incidental music composer Murray Gold
Series Series 9
Length 2nd of 2-part story, 42 minutes
Originally broadcast 10 October 2015
In the cold opening, the Doctor explains to the audience the nature of the bootstrap paradox, posing that if a time traveller recreated Beethoven's music after learning Beethoven never existed, what is the origin of the music, or "Who really composed Beethoven's Fifth?"
The Doctor, O'Donnell, and Bennett arrive in 1980, before the town was flooded and the day the alien craft landed. They meet its pilot, the Tivolian Prentis, whom they recognize as one of the ghosts in the future. Prentis had stopped on Earth while carrying the corpse of the Fisher King, a powerful warlord, to its resting place. The Doctor observes Prentis' ship still has the stasis chamber, both power cells, and the absence of glyphs on the walls.
In 2113, Cass reads the Doctor's ghost's lips to get a set of names, those of the base crew and Prentis, the Doctor, and Clara. Clara relays this via phone to the Doctor in the past, who laments he now knows his future. During this, the still-alive Fisher King escapes the stasis chamber, kills Prentis, and scratches the glyphs into the walls. O'Donnell is separated and is killed by the Fisher King, and the Doctor confirms his theory that his ghost's list is the order which they will die, and vows to save Clara who is next. Bennett, who had been in love with O'Donnell, lambastes him for using her as a test subject. When they try to return to the future, the TARDIS only sends them back a half-hour, as the Doctor is locked into his time stream. He tells Bennett to stay aboard while he goes to meet the Fisher King without changing past events.
The Fisher King, after scavenging his stasis chamber, confronts the Doctor, affirming that his glyphs and the ghosts he creates with them will send a signal that will draw an armada to conquer Earth. The Doctor says he has removed the glyphs from the ship's wall. The King runs to the ship to find the Doctor lured him away to a trap, as the glyphs are still on the walls. The Doctor had set one of the power cells to detonate and destroy the dam, flooding the town and killing the King. Meanwhile, the TARDIS transports Bennett back to the base.
In the future, Clara, Cass, and Lunn attempt to escape the Faraday cage but are cornered in the hanger bay, when the stasis chamber opens, revealing the Doctor, who had used it to survive the flood. He uses his sonic glasses, which created the image of the ghost Doctor, to lure the ghosts to the Faraday cage and trap them there until UNIT can arrive to remove it. The Doctor wipes the memories of the glyphs from everyone's minds. Bennett, still mourning his loss, convinces Cass and Lunn to admit their love for each other.
As they leave, Clara asks about the origin of the list of names he had his ghost repeat, which the Doctor replies "Who composed Beethoven's Fifth?"