Jack and Jill — John Scherber

JACK AND JILL
It's all uphill and getting steeper in Jack and Jill's marriage, until Jack discovers an easy way out. He'll simply have her eliminated while he's gone on a business trip. It's not that he's a bad guy; anyone can have a single slip up. But when the hired killer has some slip ups of his own, it looks like Jack is going down for it. Naturally, he does what anyone would do; he calls the Zacher Agency to prove his innocence.
Paul Zacher and friends end up with their least favorite client, ever.
Jack and Jill is the seventh of the Murder in Mexico series of mysteries. There is no nursery rhyme on the subject of murder.