Percival Ross was the brother of Edmund Ross, of whom he was very jealous. He obtained some Rutan healing salve from a Rutan ship that crashed in Limehouse, but left the occupant to die. He used the salve to conduct experiments on children, hybridising them with other animals. He was stopped by his brother and the Fourth Doctor. Severely injured and escaping from them, he went to his laboratory and immersed his hands in the salve. He lost consciousness as the laboratory was flooded. (PROSE: Evolution)