When a huge storm hits, Will and Dr Smith seek shelter inside a cave. The storm dislodges some rocks outside and the two become trapped. Inside the cave they discover a revolving door to another world.
Meanwhile, Don, Judy and Maureen attempt rescue from outside the cave. They eventually make their way through where they find Dr Smith. He explains Will has disappeared into a mysterious space-continuum passage to another dimension.
By reading a plaque on a wall, Will realizes he is back on Earth in Scotland during the Middle Ages. He witnesses a series of strange events while inside a castle. Will meets a ghost named Hamish who plays the bagpipes. Whenever Hamish plays the bagpipes a ghastly creature named Angus emerges from a swamp near the castle grounds.
Will comes back to the cave via the space-time continuum doorway. When he returns no one believes he has returned to Earth. Will says he he brought back with him a sample of a weed that was growing all over the Scottish castle wall and can only be found back on Earth. Dr Smith examines the weed under a microscope while at the same time consulting a plant textbook. He confirms it is a type of indigenous ivy found only in Scotland, back on Earth.
Now that they know the portal leads back to Earth, the Robinsons believe they can go home at last. The portal is limited, though, so only one person, Dr. Smith, is to return. The plan is for Smith to contact Alpha Control in order to effect the Robinsons’ rescue. Once he reaches Earth however, Dr Smith abandons the idea to pursue his own motives.
Smith’s subterfuge is foiled by both the ghost Hamish and the swamp creature Angus. Eventually he too returns back to the cave.
Irish-born actor Sean McClory (1924 – 2003) played the role of the bag-pipe playing ghost Hamish. Among hundreds of film and television appearances, he had parts in these movies –