Roberts Blossom (Gustav), Philip Bosco (Duke Michael), John Call (Customs Officer), Francis Compton (Sir Hubert Whittam), Farley Granger (Rupert of Hentzau), Mark Lenard (Detchard), Rex O'Malley (Chancellor), Christopher Plummer (Rudolf Rassendyll / King Rudolf), Roy Poole (Johann), Inger Stevens (Princess Flavia), James Valentine (Fritz Von Tarlenheim), Nancy Wickwire (Antoinette de Mauban), and John Williams (Colonel Sapt).