Parts: 2 (45-minute)
Writers: Steven Moffat
Airdate: 01 — 08 November 2014
Production Code: n/a

Doctor: twelfth
Companions: Clara

Megalomaniac of the Week: the Master
Creature Feature: Cybermen
Special Guests: UNIT

Story: When Clara suffers a sudden loss, she demands that the Doctor intervene to change history. Although he is unwilling, or unable, to cross that line, he does agree to help... by trying to find the human afterlife.

His search brings the TARDIS to 3W, an advanced facility where the deceased are housed in water tanks, an apparently protective measure designed to alleviate their clients' fears... of what? The Doctor is also introduced to Missy, the founder of 3W, who — unbeknownst to him and Clara — has been monitoring his recent adventures. What is the true purpose of 3W? What horrific secrets does it hide? And who exactly is the enigmatic Missy?