Parts: 2 (45-minute)
Writers: Steven Moffat
Airdate: 19 — 26 September 2015
Production Code: n/a

Doctor: twelfth
Companion: Clara

Megalomaniac of the Week: Davros, the Master
Creature Feature: Daleks
Special Guests: UNIT

Story: Throughout the universe, a mysterious cloaked man roams in search of the Doctor. His mission: to bring the Doctor to his master Davros, who has an urgent message for him. But nobody knows where the Doctor is: not his friends across space and time, not UNIT, not even Clara. And not Missy, who solicits Clara's assistance to track him down, after receiving word that the Doctor is about to die.

The Doctor's disappearance can be traced back to an alien world caught in a massive multigenerational war, and his attempt to help a young boy in peril on the battlefield. After the events of that day, the Doctor goes into hiding... but what has the Doctor done that causes him to feel so ashamed?