The Doctor and Jo are trapped on the fort by a Sea Devil while the Master convinces Trenchard to help him steal some electronic components.
Quest roles:
Edwin Richfield(Mestor), Terry Walsh(Doran (uncredited)), Pat Gorman(Pilot), Roger Delgado(The Master), Eric Mason(C.P.O. Smedley), Clive Morton(Trenchard), Declan Mulholland(Till), June Murphy(3rd Officer Jane Blythe)