Based on the novel by Edgar Wallace, detectives at Scotland Yard try and track down The Crimson Circle, a secret society of blackmailers

London's jewel thieves are under the thumb of a mysterious fence, who ruthlessly exposes any thief who crosses him. Desperate, Scotland Yard re-hires ex-Inspector Barrabal who, as a known drunkard, is ideally suited to go undercover with a faked criminal record (which may spoil his chances with lovely Carol Stedman).

Sensuous and desirable, Carol Forrest has always attracted the attention of men. Expert in the art of manipulation and control she married an older man, loving only his vast wealth and continued to amuse herself with indiscreet affairs. But when neighbour Mark Kendrick lets slip that her husband intends cutting her out of his will Carol concentrates all her attentions on the unsuspecting Kendrick, obtaining his help to dispose of this irritating obstacle.

A man murdered at the Saint's doorstep manages to utter a few words to Simon Templar before he dies, sending him off to the quaint resort village of Baycombe where he confronts crime mastermind 'The Tiger' and his gang as they plan to smuggle gold bullion out of the country.

While on vacation, the Saint discovers a much-sought-after music box.

Suave soldier of fortune Simon Templer gets mixed up with a gang of counterfeiters who've murdered and robbed an European count of 1,000,000 pounds. He is aided reluctantly by Scotland Yard inspector Teal, who's convinced that Templar himself pulled off the heist, and less reluctantly by light-fingered Dugan and dizzy socialite Penny Parker.

In England, an eccentric police inspector, an earnest test pilot and a spunky female reporter team up to solve the mystery of a series of test aircraft which have disappeared without a trace while over the ocean on their maiden flights; unaware, as they are, that a spy ring has been shooting the planes down with a ray machine hidden aboard a salvage vessel which is on hand to haul the downed aircraft aboard, crews and all.