After the death of his wife Robert Turold, a hard and bitter man, is just one step away from proving his noble linage and claim to a great estate. This is his life-long dream and the last obstacle to achieving it is his despised daughter Sisily, whom he intends to disinherit. But just as he is about to reach his dream he is found shot dead in a room locked from the inside. The mysterious death may look like a suicide at first but Detective Barrant and Inspector Dawfield suspect that the truth is more complicated and are determined to solve the puzzle.

This fast-paced detective story unfolds through the tangles of complicated family ties and secrets, suspicious servants, and a mysterious Cornish legend. The Moon Rock was first published in 1922.