When a pearl with a sinister reputation for causing misfortune to its owners is stolen from a museum by a master criminal because of Sherlock Holmes' show-boating, he is naturally obliged to find it. Soon, he learns of a series of brutal murders that seemed to have been commited by a malevolent man mountain known only as the Creeper. Now, Holmes must deal with the seemingly overwhelming menace of this man and his boss in order to retrieve the pearl.

England, at the start of World War Two. Mysterious wireless broadcasts, apparently from Nazi Germany are heard over the BBC. The warn of acts of terror in England, just before they take place. Baffled, the Defence Committee call in Holmes ...