The BBC Media Centre has released the official synopsis for the ninth episode of the current series of Doctor Who, read on for further details:
FLATLINE - by Jamie Mathieson
Separated from the Doctor, Clara discovers a new menace from another dimension. But how do you hide when even the walls are no protection? With people to save and the Doctor trapped, Clara comes up against an enemy that exists beyond human perception.
Doctor Who: Flatline will broadcast Saturday 18th October at 8:25pm on BBC One and BBC One HD.