Around the turn of the century, in England, alcoholic Uncle Willie is the bane of his family, of which his brother-in-law is the family spokesman. It is decided to let Uncle Willie buy a bicycle shop in order to impress Virginia van Stuyden, an American heiress in love with Frank. This pleases Uncle Willie's young nephew, Charles. Complications arise when stuffy lord, Sir George Probus, at whose home Virginia is staying, becomes shocked when she attends a carnival.
American professor John Holden arrives in London for a conference on parapsychology only to discover that the colleague he was supposed to meet was killed in a freak accident the day before. It turns out that the deceased had been investigating a cult lead by Dr. Julian Karswell. Though a skeptic, Holden is suspicious of the devil-worshiping Karswell. Following a trail of mysterious manuscripts, Holden enters a world that makes him question his faith in science.
Two men working on the docks close to London's Tower Bridge find the body of an unidentified man floating in the Thames. The police later identify the body to be that of a diamond courier from Holland. The police have to find his murderer, as well as the missing diamonds he was carrying.
The dining room of the Jolly Fiddler has long been presided over by Albert, an aged but very shrewd waiter. A past master of the gentle art of fiddling, he extracts the maximum profit from his job while managing to endear himself to both the customers and staff. Then, there's a visit from Mr Finch, who feels it's time Albert was replaced.
