Ghost story writer Professor Dunning (Terry Molloy) doesn't believe in the supernatural. So he's more than surprised when an invisible winged demon appears in his drawing room.

The Metropolitan Police's longest-serving officer, Inspector Lionheart (Nicholas Courtney), doesn't believe in the supernatural either, wings or no wings. So he's less than impressed when Russian emigres begin dying impossible deaths all over London.

So begins a series of wry adventures for Professor Dunning and Inspector Lionheart as they face mummies, robots, the undead and an inter-dimensional being from the dawn of time.