Sarah and Gemma appear in a flash in a medieval market place. They spend some time exploring the town and observing the cliched antics of the locals. Meanwhile, some guards taunt a mad old man in the castle dungeons, which are infested with at least three rats. Count John (Aubrey Woods) goes into a tower and confronts his cousin, Lady Eleanor (Sheila Dunn). She is furious that he has kept her prisoner for so long and demands to be released so that she can marry Sir Robert. John gloatingly says that Robert has been banished. Eleanor will never marry, and when she dies, John will inherit her land.
Sarah and Gemma continue to explore. They see a mysterious hooded figure and chase it into the cathedral. The figure vanishes but Sarah and Gemma meet Bishop Godfrey (Timothy Bateson), who tells them that the city is haunted by demons because of the Count’s misrule. The Bishop asks Sarah and Gemma to help him by taking a message to Lady Eleanor.
Inside the castle, the captain of the guard (Ron Peaklow) tells the Count that outlaws are causing trouble. The jester (Ian Slaith) makes a surprisingly risque joke about a “stupid count”, and the Count kicks him. Sarah and Gemma sneak into the castle and come face to face with a hooded figure. Gemma pulls down the hood to reveal a hideous Martian face (Ted Furnage again, in green makeup).
Gemma is captured and thrown into the dungeon, but Sarah uses her psychic powers to trick the guards and gets away. She sneaks into the tower and delivers the Bishop’s message to Eleanor, who says she must find Sir Robert.
The Count has a blazing row with the Martian leader (Norman Jones) about who is in charge. Sarah tries to get to the dungeon but there are two Martians in the way, so she slips out of the castle in disguise. Gemma escapes and spends some time running around the castle but is eventually caught and put back in the dungeon. The Martian leader says that Gemma must be killed immediately, but the Count refuses. He says they need to split the Bishop from Eleanor. Gemma must be publicly executed for witchcraft so that the Bishop cannot support her and her friends.
Sarah goes into the woods looking for Sir Robert and is captured by outlaws. She recaps the plot to the outlaw leader, whose face is hidden by a hood. He agrees to help rescue the prisoners from the castle. Gemma is tried and convicted on spurious grounds. She is tied to a stake in the marketplace to be burnt alive.