Deep 13 was a subbasement of Gizmonic Institute and, according to former SOL janitor Joel Robinson, highly radioactive as a result of being close to the Institute's atomic pile. The Mads worked and eventually took up residence there as well. There was a neighboring Deep 12 whose tenants once included two "foxy ladies." Two resident Mole People, Gerry and Sylvia (named after Gerry and Sylvia Anderson), also served as Dr. Forrester and TV's Frank's assistants in Season 2 and Season 3.