The BBC has released the official story synopsis for Under the Lake, the third episode of Series 9.

When an underwater base comes under attack, the Doctor and Clara must save the frightened crew and defeat an impossible threat. But what is behind these terrifying events? And can they really be haunted by ghosts? Writer: Toby Whithouse. Director: Daniel O’Hara. Producer: Derek Ritchie.

Cast: Peter Capaldi and Jenna Coleman

Guest cast: Colin McFarlane, Sophie Stone, Zaqi Ismail, Morven Christie, Arsher Ali, Steven Robertson, Paul Kaye.

It airs Saturday 3 October on BBC One, with the time now confirmed for 8.25pm to 9.10pm.