One night Epsilon Delta left in the waiting TARDIS and became a renegade Time Lord after using his spare time to secretly adapt the ship to his palm and voice prints since he had enough time on his hands to study in the archives which was one of the benefits to his tedious job as the assistant to the Gold Usher, and to find a TARDIS to take him away.
As he left Gallifrey, he monitored the security channels and found it ironic that the Time Lords cared more about him stealing such an advanced TARDIS than they were about him. Epsilon Delta travelled to Argolis and Earth in the TARDIS. During one of his trips, he had a run-in with some Sontarans, which triggered his first regeneration. Later he found out the TARDIS was shrinking due to the Garvond, whom he allied himself with in order to repair his ship and give it a burst of energy.
Epsilon Delta found many aspects of his TARDIS to be attractive, most notably its voice-activated lock, and the reliable chameleon circuit, which disguised the ship either as a sports car or a filing cabinet. He also played chess against the ship.
The interior of the TARDIS was primarily burgundy, with the console in the shape of an upturned cone with a flat top, with a spiralling central column with touch-sensitive controls. The roundels were more compact and closer together than those on the Doctor's TARDIS.