"The Unknown" was the final entry in Columbia’s I Love A Mystery series. A woman hires two detectives to keep her alive long enough to claim her inheritance.
An investigator from the War Crimes Commission travels to Connecticut to find an infamous Nazi, who may be hiding out in a small town in the guise of a distinguished professor engaged to the Supreme Court Justice’s daughter.
After three men are convicted of bank robberies, Charlie becomes suspicious. After some investigation Charlie finds the men are innocent and that the fingerprint evidence used to convict them had been forged. Charlie then proceeds to find the true bank robbers.
A convicted thief in Dartmoor prison hides the location of the stolen Bank of England printing plates inside three music boxes. When the innocent purchasers of the boxes start to be murdered, Holmes and Watson investigate.
London, 1761. St. Mary's of Bethlehem, a sinister madhouse, is visited by wealthy people who enjoy watching the patients confined there as if they were caged animals. Nell Bowen, one of the visitors, is horrified by the deplorable living conditions of the unfortunate inhabitants of this godforsaken place, better known as Bedlam.
Holmes and Watson board a passenger train bound from London to Edinburgh, to guard the Star of Rhodesia, an enormous diamond worth a fortune belonging to an elderly woman of wealth; but within the first hour of the trip, the woman's son is murdered and the diamond stolen and any of the passengers in their car could be the killer thief.
Sherlock Holmes investigates when young women around London turn up murdered, each with a finger severed. Scotland Yard suspects a madman, but Holmes believes the killings to be part of a diabolical plot.
Edinburgh, 1831. Among those who undertake the illegal trade of grave robbery is Gray, ostensibly a cab driver. Formerly a medical student convicted of grave robbery, Gray holds a grudge against Dr. MacFarlane who had escaped detection and punishment.
In 1903, Doctor Huntington Bailey meets a friendly older lady during a train trip. She tells him that she is going to visit her brother Nick and his lovely young wife Allida. Once in New York, Bailey hears that his train companion suddenly died. Shortly afterward, he meets the strange couple and gets suspicious of Nick's treatment of his wife.
The famous Borgia Pearl, a valuable gem with a history of bringing murder and misfortune to its owner since the days of the Borgias, is brought to London, thanks in part to Sherlock Holmes. But before long the jewel is stolen, due to an error on Holmes' part, and shortly thereafter, a series of horrible murders begin, the murderer leaving his victims with their spines snapped and surrounded by a mass of smashed china.