As the Saveteem and Tesh finally close in for a fight to the death, the powerful but long-suffering Xoanon ignores their strife to commit its full resources toward killing the Doctor, even to the extent of destroying everyone.

As the strangulations continue and the humans aren't sure who to blame, Leela meets up with an anomaly among the robot crew - an inquisitive, supposedly mute single-function labor robot capable of independent reasoning. Meanwhile the Doctor starts looking into the possibility that the murderer is a robot, and another crew member is targeted for death.