Sir Henry Merrivale

James Bennett, nephew of Sir Henry Merrivale (the cantankerous yet genius sleuth), has been invited to stay at White Priory for Christmas, among the retinue of the glamorous Hollywood actress Marcia Tait. Her producer, her lover, her playwright and her agent are all here along with the haughty master of the estate, Canifes and his daughter. So many suspects they become when Marcia Tait is found dead on Christmas morning in the lakeside pavilion, having been left there alone the night before and with a distinct lack of footprints in the snow to reveal any possible killer.

The diplomat Sir George Ramsden is returning to Britain from France with the mysterious 'unicorn' in tow. The legendary thief Flamande has declared that he will be on the same flight as Ramsden, in disguise, and that the unicorn will be his. His arch-rival and head of the Sûreté Nationale, Gasquet, has assured the public that he too will be on the plane to thwart his nemesis. Meanwhile, holidaying in Paris, the ex-spy Kenwood Blake runs into Evelyn Cheyne and is swept into a perilous chase ending at the Chateau de l'Île on a stormy night.

On the eve of his wedding to Evelyn Cheyne, who he met and fell in love with during the course of The Unicorn Murders, former spy Kenwood Blake is summoned to Devon by spymaster Sir Henry Merrivale, and asked to take part in an undercover operation. Once in Torquay, he is sent to investigate Paul Hogenauer, a local scientist of German heritage, who has been dabbling in spiritualism and the occult – a man Merrivale and Devon's Chief Constable Colonel Charters suspect of anti-British espionage.

'There will be ten teacups at number 4, Berwick Terrace, W.8, on Wednesday, July 31st, at 5 p.m. Precisely. The presence of the Metropolitan Police is respectfully requested.' The note was delivered to New Scotland Yard, its words evoking a cold murder case and its unsolved mystery of the ten teacups found beside the body. Scrambling to prevent a second killing, the police set up a watertight cordon at Berwick Terrace. But gunfire rings out from the top floor at 5 p.m.

One of the greatest locked-room murder mysteries of all time, hailing from 1938, returns to baffle a new bevy of armchair detectives. James Answell, visiting his father-in-law Avery Hume in his locked study, has the misfortune to wake up from a drugged-Whisky swoon to find his host dead, skewered with an arrow. He is, of course, prime suspect.