The Three Beans

The Three Beans a.k.a. The Birdwatcher's Quarry by Manning Coles is a spy thriller novel which follows the adventures of Thomas Hambledon, the British foreign intelligence operative.
The title stems from a crucial piece of physical evidence used to solve the crime—literally, three beans.

In this story, an accidental death turns out to be a highly calculated murder. Tommy Hambledon investigates a dangerous gang after a young intelligence operative brings a case to his attention.