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. (AUDIO: Collateral)