The Doctor and Jo are brought to Prague in 2221 against their will by an old acquaintance of the Doctor's, Benek Chaloupka, a former magician. He used to use a pair of Psion orbs in his act until one of them was broken. He now runs a museum called Marvels Less Mystifying that seeks to debunk things like magic, superstition and the occult. However, to his embarrassment, his museum is haunted by ghosts.
The Doctor explains to Jo that Prague at this time is built on seven levels, with the lowest level housing the undesirable people — criminals and addicts.
As the Doctor and Jo investigate the museum, the Doctor rules out energy fields and holograms. They split up — the Doctor needs equipment from the TARDIS while Jo goes to Chaloupka's office. There she is confronted by several different ghosts, terrifying her. The Doctor also encounters ghosts, and is even attacked by a boy with a knife — who is not a ghost. The Doctor realises he must be protecting something and follows him to the lowest level of the city.
The boy was protecting a sleeping girl. When she sees the Doctor she runs away, but he steps on a Psion orb. The orb had been projecting the dreams of the two children while they slept.
The mystery solved, Jo and the Doctor leave. The Doctor is annoyed because he knows Chaloupka could have solved the problem on his own and was merely using the situation as a publicity coup.
- Prague is part of the Third Czech and Slovak Republic.
- The Doctor listens to "Coz I Luv You" by Noddy Holder.
- In Jo's time, the president of Czechoslovakia is "Mr Svoboda".
- Jo finds graves for Jan Neruda and Max Svabinsky in the Vysehrad Cemetery.
- Benek mentions that the Doctor has regenerated.
- Wax figures in the museum include Nostradamus, Bigfoot, and the Golem of Prague.
- Jo sees an exhibit for the Mary Celeste.
to be added