Transmission: 03.10.2015/ 10.10.2015.

Writer: Toby Whithouse.

Director: Daniel O'Hara.

Guest Starring: Morven Christie; Colin McFarlane; Sophie Stone; Arsher Ali; Peter Serafinowicz; Zaqi Ismail; Steven Robertson; and Paul Kaye.

It's 2119 and a mining crew discovers a spaceship and hauls it aboard their underwater base. When the Doctor and Clara arrive, the base is plagued by hollow-eyed ghosts – but as the Doctor says, "They're not ghosts; we're not nine years old." So what really are they? What are their intentions? And is it possible to meet you own ghost?

The time-travellers have a several more questions: "What’s death like? Does it hurt? Do you still get hungry? Do you miss being alive?"

Teased as having elements of The Impossible Planet/ The Satan Pit (2006), 42 (2007), and 2009's The Waters of Mars, the action then moves a few hundred years into the past, where, on a remote army outpost, the Doctor must stop the seemingly-inevitable as an alien warlord, the Fisher King, tries to ensure its own future.

This is the first base-under-siege story for a while, but there's a timey-wimey twist, while writer, Toby Whithouse told Doctor Who Magazine: "Death is the one thing which defines every single species... And what the Doctor finds so fascinating about [the creatures in this two-part tale] is they seem to have overcome this one limitation that every single lifeform has. Every sane person would regard that as terrifying, but to him, it's fascinating."

It's a welcome return for Whithouse, who has worked on Doctor Who since 2006 when his debut episode, School Reunion, reintroduced Sarah Jane Smith and K9. His last episodes was 2012's A Town Called Mercy, but it's actually a race created for The God Complex (2011) that briefly gets revisited in this two-part tale: Paul Kaye (Ripper Street; Game of Thrones) plays Prentis, a native of Tivoli (aka the most invaded planet in the galaxy!

Whithouse is reunited with Daniel O'Hara, whose worked on two previous franchises created by the writer: Being Human and last year's The Game. This is O'Hara's first gig on Doctor Who, but he's also directed four 2012 episodes of Wizards vs. Aliens, the family series created by former Who showrunner, Russell T Davies, and Into the Dalek writer, Phil Ford.

The Fisher King is voiced by Peter Serafinowicz (Shaun of the Dead) – his scream provided by Skipknot's CoreyTaylor – but the alien itself is from Arthurian legend. He's the last in a long line to protect the Holy Grail, a relic supposedly with special powers: it has the ability to give eternal youth...

Ghosts. An underwater base-under-siege. Questions about immortality. Time travel. This is Classic Doctor Who at its finest...

Under the Lake airs tonight on BBCOne at 8:25pm.