At first I found the setting of this mystery to be quite interesting. The landscape is dramatic. That said, the solution to the mystery, the how, is deceptively simple. The who is rather unsatisfying, as the killer's character is not as developed as it could be. The side-plot about WWII spies operated at such a level of simplicity as to be somewhat absurd. A significant part of this mystery is figuring out how, exactly, Alleyn will come to be involved. I had that part figured about well before the end. This is not the best of Marsh's work. Her New Zealand mysteries never are.
Ngaio Marsh, Colour Scheme (orig. 1943) ISBN: 1937384551