Zachary was present on Skaro on the day of Operation Starbug and was assigned to oversee the robotisation of prisoners whilst the Dalek security force dealt with an escape attempt. It was during one of these robotisations that Juliet was sent to, having proven herself to have superior mental capacity than the other prisoners. Juliet, having heard about the captured Starbug, attempted to persuade Zachary to help her escape; Zachary, however, was more interested in preserving his own life, using the Dalek facilities and "things we don't talk about in children's programs", and refuses. Before Zachary could convert Juliet, however, a Polymorph, one of the Daleks' genetic experiments, broke into the test lab and became ensnared in the machine with Juliet as Zachary started the process. At that same moment, Captain Maloney broke into the room and forced Zachary to direct him to the intercom at gunpoint, in order to coordinate the uprising and direct the survivors to the ship. As Juliet manages to get out before being brainwashed and was somehow merged with the Polymorph, the first thing she does is use her newfound Polymorph abilities to pin Zachary to the wall with sticky webs. When she and Maloney notice each other, they quickly forget about Zachary and go to escape together, leaving Zachary to his fate.
As Zachary was ensnared by the webs, it is unlikely that he managed to escape before Skaro was destroyed by Starbug.
Zachary was utterly depraved and self-serving, only interested in his own gain.
Zachary was one of the first people to note that Daleks tie their prisoners to chairs, despite not having any need for them themselves.