With Peter Capaldi, Jenna Coleman, Joivan Wade, Samuel Anderson. But the Doctor is a one-liner machine in “Flatline,” as the script marries this incarnation’s usual aloofness with the mounting impotence of his situation to great comic effect. A problem happens with the Tardis, trapping the Doctor inside and leaving Clara to fend for herself against a two dimensional enemy. Directed by Douglas Mackinnon.