Jon Pertwee as The Doctor

Caroline John as Liz Shaw

Nicholas Courtney as Brigadier Lethbridge-Stewart

Ronald Allen as Ralph Cornish

John Abineri as Carrington

Robert Cawdron as Taltalian

Michael Wisher as John Wakefield

Cheryl Molineaux as Miss Rutherford

Ray Armstrong as Grey

Robert Robertson as Collinson

Ric Felgate as Van Lyden / Alien Ambassador

Dallas Cavell as Quinlan

Bernard Martin as Control Room Assistant

John Moreno as Dobson

James Haswell as Corporal Champion

Derek Ware as UNIT Sergeant

William Dysart as Reegan

Cyril Shaps as Lennox

Gordon Sterne as Heldorf

Steve Peters as Alien Ambassador / Lefee

Neville Simons as Alien Ambassador / Michaels

Max Faulkner as UNIT Soldier

John Lord as Masters

Tony Harwood as Flynn

John Levene as Sergeant Benton

James Clayton as Private Parker

Joanna Ross as Control Room Assistant

Carl Conway as Control Room Assistant

Roy Scammell as Technician

Peter Noel Cook as Alien Space Captain

Peter Halliday as Aliens' Voices

Geoffrey Beevers as Private Johnson