Prydonian Academy Revolution

The Prydonian Academy Revolution was an attempted coup fomented by the Master shortly before he and the Doctor were forced to leave Gallifrey, which involved organising an uprising of the students of the Prydonian Academy. The plot was exposed by the Doctor, forcing the Master to begin his plan early; in the ensuing chaos, a wounded Master fled Gallifrey in disgrace while the Doctor went on the run with Susan Foreman. (PROSE: Birth of a Renegade, CIA File Extracts)