Captain Douglas Cavendish was a member of the Virtual Ordnance Group at UNIT. He was sent to investigate the explosion at the Det-Sen Monastery, where he came in contact with some web made by the Great Intelligence and came under its influence.
Back in England, he tried to find out from the Brigadier if he had any alien souvenirs from his old UNIT days. He later stole the reports of the initial Yeti encounter. (HOMEVID: Downtime, PROSE: Downtime)
After being freed from the Great Intelligence, he left UNIT. Kate Stewart visited him at his country home, where he felt he was being stalked by a statue. He was being influenced to summon a Dæmon named Mastho by future forces trying to affect the past. He and Stewart managed to stop them. (HOMEVID: Dæmos Rising)