Lucy Durmast is on trial for murder but she is taking her right to remain silent to extreme lengths and refuses to say anything - even to the extent of refusing to plead guilty or not-guilty. Her friend Kenneth died of poison shortly after eating a meal which she had cooked and served to him.Sloan and Crosby are given the task of reviewing what seems like an open and shut case because the original investigating officer is ill. Sloan is not convinced that Lucy is guilty but he cannot at first see who else could possibly have had means motive and opportunity.Obscure African countries, civil engineering projects and a thoroughly ingenious method of murder makes this an interesting and entertaining read. This is one of Catherine Aird's excellent Sloan and Crosby series which I don't believe I'd read before. It is, in my opinion, one of the best in this excellent series and I defy anyone to work out who did it and why.