Harriet Vane fresh from being acquitted of a murder charge is rambling along the coast where she finds the body of a male who has recently had his throat cut.
Soon after Lord Peter Wimsey arrives to support her and to attempt to get her to marry him. Along with the local police the couple set about solving the mystery of the body on the rock.
This is a very clever plot, if you read it carefully all the clues are there especially for the real history buff. I didn't get close to figuring out how it was done. A top read and very good mystery.