Doctor Who: Four to Doomsday (1981)

Another adventure for everyone's favourite Time Lord. When the TARDIS makes an unscheduled landing on a mysterious spacecraft heading towards planet Earth, the Doctor (Peter Davison) and his cohorts are surprised to find that the crew members are drawn from a variety of ancient Earth cultures. Their leader, however, is a frog-like alien known as Monarch (Stratford Johns), and the more the Doctor finds out about his plans for the future of Earth, the less he likes them.