- You may be looking for the control node of the SS Madame de Pompadour.
A control node was a unit found in a group of Clockwork Droids who served as their leader. Without the control node, Clockwork Droids were unable to function and shut down. One such control node was the Half-Face Man, who over the course of millions of years had integrated human physiology into his makeup. (TV: Deep Breath)