Blake Nicholas Blake 
Penknife in My Heart 

First published in 1958, A Penknife in My Heart tells the story of how two men – total strangers – establish the perfect alibis by arranging to switch victims. Ned Stowe will kill Stuart Hammer’s wealthy uncle for which service Hammer is to eliminate Stowe’s neurotic wife, Helena. The men plot and the plan – with its horrifyingly simple premise – is solidified…’More convincing, more detailedly thought-through than Highsmith’s [Strangers on a Train].’ – The New York Times