J. S. Fletcher, centering on why a former high-level police official was murdered, and on whether - and if so how - the murder was linked to two glamorous and high-profile sisters, one of whose photo was found in the dead man's pocket. As usual, Fletcher creates a number of different detectives -- a lawyer, his assistant, several policemen, a police spy, and even the dead man's granddaughter -- following various lines of inquiry. These lines converge rapidly in the last few chapters, when the author lets the reader weave them together into a coherent whole: the solution to the mystery.