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 Ministry of Defence report of the initial Yeti encounter. (HOMEVID: Downtime, PROSE: Downtime)
After being freed from the Great Intelligence, Cavendish left UNIT. In October 2003, Kate Stewart received a message from Cavendish, asking her to visit him at his country home, where he felt he was being stalked by a statue of a demon-like creature, as well as encountering a ghost-like figure in the house. It transpired that Cavendish was being influenced to summon a Dæmon named Mastho by forces from the future trying to affect the past, but he and Kate managed to stop them. (HOMEVID: Dæmos Rising)