Jamie Mathieson clearly had a good time writing last week's Mummy on the Orient Express, because the former Being Human writer is already back with another entry for Doctor Who - this time the episode going by the name of Flatline. This time the Doctor takes a bit of a backseat as he becomes trapped in a shrinking (well, on the outside anyway) TARDIS - it's power being siphoned away by an mysterious alien entity. It's up to Clara to take up the role of the Doctor and investigate, connecting it with the disappearance of a number of people in the estate they've landed in. After discovering that the threat is not of the third dimension - Clara learns first hand about what it's really like to play the Doctor.