Chisholm was the chief engineer of the GSO drilling project that accidentally uncovered the Cybermen's ship.
Cybermats were released by the ship's computer and began attacking the crew and infecting them with a nanovirus which would result in their cyber-conversion. He escaped on vehicle, but crashed in a cave, where the Eleventh Doctor and Amy had just arrived. The Doctor saved him by warming up some water with his sonic screwdriver and giving it to him to prevent hypothermia. Thanks to the Doctor finding an alternate path back up to the TARDIS (due to a sprained ankle), Chisholm explained what happened and much to his shock (after seeing the inside of the TARDIS), he found that they had taken him back to the base. There, he was attacked by a Cybermat and bitten; he locked himself in a tower to prevent himself from hurting Amy and the Doctor when he changed. Though they didn't listen to him, Chisholm gave them tidbits of advice on how to find things they needed to repair the base and help Elizabeth Meadows in finding a cure. When they brought the cure to him (after Meadows had vanished), he was least partially converted into a Cyberslave. Taking the antidote, he lead them to the elevator that lead to their excavation site; he had to stay behind as his body was in too much pain from the process reversing itself. He later saved the Doctor and Amy by using an amputated Cyber-Arm to shoot three Cybermen who were advancing on them. (GAME: Blood of the Cybermen)