The Doctor and Clara find themselves deep underwater this week where they're attacked by an army of creepy hollow-eyed ghosts in a terrifying new two-part adventure. It's the year 2119 and the TARDIS has landed inside The Drum, an underwater mining facility in Caithness, Scotland that lies in a valley that was flooded when a dam was built there… When the pair catch up with the Drum’s crew – Bennett (Arsher Ali), O'Donnel (Morven Christie), Lunn (Zaqi Ismail), Pritchard (Steven Robertson) and Cass (Sophie Stone) who’s deaf, - they learn about the terrifying events of a few days before.
On the bed of the lake, the crew of The Drum had discovered some sort of spaceship, which they'd then brought into the base. Soon afterwards, however, the ship sparked into life which ended up killing the base commander Captain John Moran (Colin McFarlane). Moran was turned into a zombie-like ghost who proceeded to stalk the crew together with another deadly apparition - a mysterious ghost with a top hat called Prentis (Paul Kaye).
When the Doctor eventually gets to examine the mysterious spaceship, he begins to piece together clues to found out where it came from and the secrets behind the ghosts, but not before another of the Drum's crew, Pritchard, is killed, drowned by the ghosts!
There are some 'timey-wimey' style explanations behind everything it seems. When the Doctor and Clara become separated, the Doctor decides to take the TARDIS back in time to before the Scottish valley was flooded by the dam. But no sooner has he left, Clara gets the shock of her life in 2119 - she sees the Doctor floating underwater as one of the creepy hollow-eyed ghosts!
