He was a metamorph. When Montague ordered Jean Veber to kill Emil in retaliation for the theft of the Doll's House, Veber ran him over with a carriage. However, he was able to transfer his mind into Veber, saving himself from being crushed to death. His metamorphic powers changed the body he was inhabiting until it looked like his old one.
Later, with the help of the Seventh Doctor and the TARDIS, he was able to communicate with the Quoth within him. Learning of the harm he and the other psychics they were living in were causing them, he promised to help the Quoth. (PROSE: The Death of Art)