I wouldn't describe The Last Wife as a crime novel per se; although within the course of the journey, a few people do come to an untimely end. It is told by the protagonist, a young(ish) single woman, named Marie, and is a dark journey.
Everything in the convoluted plot stems from a holiday in Ibiza shared by Marie, her best friend Nina, Nina's boyfriend [and subsequent husband] Stuart, Marie's boyfriend Charlie, and Nina's friend Camilla [from some years ago]. Towards the end of their holiday Nina, Camilla and Charlie took a trip out in a motor boat (Marie was not present), during which Charlie somehow fell overboard and drowned.
The key element throughout the book is Marie's relationship with Nina, who was her best friend at school and art college. Marie is now a photographer, and her work form an important ingredient to this novel. Marie is a clingy sort of person; jealous of anyone else, male or female, who becomes close to Nina. Following her marriage to Stuart, they soon have two children. Marie's greatest wish is to have a child herself with her current boyfriend, Ben - but to her chagrin she seems unable to conceive. Sadly, Nina contracts an incurable cancer and dies about a year later. Shortly before her death Nina makes Marie promise to look after her family and make sure that if Stuart marries again, it is to the right person.
Ben is getting tired of his entire relationship with Marie now revolving around conceiving a child and eventually leaves her. Then Camilla, who has been living in Canada, returns with her teenage daughter, Louise. Marie suspects that Camilla has designs on Stuart and realises that the only way to prevent their marriage is to seduce Stuart, and there hangs the tale.
The moral of this sorry tale, as is indeed mentioned in the book, as a motif - “Be careful what you wish for”.
