Eris's TARDIS

Eris stole a TARDIS and fled from Gallifrey to become a renegade Time Lord shortly after Ysalus had been destroyed in order to save himself from Rassilon and Mantus after he had spent a year there helping Knyla Shen begin an evacuation. At the same time during the year he had been there, he incited a resistance against the Time Lords who were planning on destroying Ysalus.

Romana urged Eris to steal the TARDIS, although Eris told her he couldn't just steal a TARDIS and leave. Romana told him he could and that he would not be the last. (AUDIO: Collateral)