This is not exactly a typical Dick Francis book. The protagonist, Ian, is the estranged son of a wealthy but cantankerous patriarch, Malcolm. Malcolm's fifth wife has just been murdered, and Malcolm fears (correctly) that he's next. Ian gets dragooned into playing detective, and he needs to sort through the motives and alibis of a host of stepbrothers, stepsisters, and stepmothers. And Malcolm seems determined on irrationally squandering his fortune, enraging his would-be heirs.
It sounds almost as if we're in Agatha Christie-land here, and that could have happened, but Francis has a good conservative eye for character and its flaws. Most of the family is in various states of dysfunction, crippled by jealousy, greed, and resentment; Francis does a fine job of painting each character as a real person, not simply a plot device.
In short, another good novel from Dick Francis.