Eris's TARDIS

Eris stole a TARDIS and fled from Gallifrey after spending a year helping Knyla Shen on Ysalus and founding a resistance against the Time Lords, making him an enemy of.

Romana II urged Eris to steal the TARDIS, which he initially refused to do. Romana, however, pointed out that he would not be the first Time Lord to steal a TARDIS and leave. (AUDIO: Collateral)