Peter Davison Doctor Who Actor Sarah Sutton Nyssa Actor Janet Fielding Tegan Jovanka Actor Mark Strickson Vislor Turlough Actor Nicholas Courtney Brigadier Lethbridge-Stewart Actor David Collings Mawdryn Actor Valentine Dyall Black Guardian Actor Angus MacKay Headmaster Actor Stephen Garlick Ibbotson Actor Roger Hammond Dr Runciman Actor Peter Moffatt Director Peter Grimwade Writer John Nathan-Turner Producer