Colour Scheme, published in 1943, is Ngaio Marsh's twelfth Roderick Alleyn novel and she regarded it as her very best. It is set in New Zealand during World War II and creates a wonderful sense of place. This, and the next book in the series, 'Died in the Wool', are both about counter-espionage in New Zealand.
The authorities suspect Nazi activity at a hot springs resort on the coast of New Zealand's North Island. Alleyn is working for military intelligence and is involved in counter-espionage. A gruesome murder takes place - Maurice Questing is lured into a pool of boiling mud and left there to die - which may or may not involve spies. Much of the book's action takes place with no mention of Alleyn and only at the end of the book is the reason revealed. The very unpleasant Questing had many enemies, including the Claire family(from whom he is trying to take the spa), English expats, Maoris and spies whom he had thwarted. He could even be a spy himself...
Ngaio Marsh was brilliant both at creating character and at creating a sense of place. Her deep love of New Zealand is very evident in this novel, as in her two other novels set in her native country. The spa on North Island, run by the Claire family, is built around antipodean natural hot mud pools and is close to a Maori village. Its leader is an aged, retired Member of Parliament; he is an attractive character whose relationship with the Claire family sheds light on their characters.
Tightly plotted, witty, moving at a good pace, this is a very good book. In some ways, it is quite dark, but as always in Marsh's books, it is redeemed by her lively wit and marvellous ability to create lively and fascinating characters.