''Shadow on the Wall'' notably, is the first full-length novel to feature the author's most famous character, the medically-qualified amateur detective Reggie Fortune, following dozens of highly successful short stories.

Mr. Reginald "Reggie" Fortune is a plump, drawling, luxury-loving Harley Street surgeon who serves as a special advisor to Scotland Yard.

Billed as Fortune's longest and most dangerous case, the story begins deceptively with the apparent suicide of a Mrs. Poyntz and an upscale garden party at Buckingham Palace. As the bodies pile up—totaling seven deaths via poison, shooting, and other means—Fortune must piece together a trail of highly erratic clues:

A fleeting, flickering shadow on a wall.
A young woman poisoned by morphia tablets that weren't actually morphia.
A perfumer in Switzerland selling a scent called Le Matin d'un Faune.
A dead monkey.