Don't Let Him In (original) Lisa Jewell

Nina Swann is intrigued when she received a condolence card from Nick Radcliffe, an old friend of her late husband, who is looking to connect after her husband’s unexpected death. Nick is a man of substance and good taste. He has a smile that could melt the coldest heart and a knack for putting others at ease. But to Nina’s adult daughter, Ash, Nick seems too slick, too polished, too good to be true. Without telling her mother, Ash begins digging into Nick’s past. What she finds is more than unsettling…

Martha is a florist living in a neighboring town with her infant daughter and her devoted husband, Alistair. But lately, Alistair has been traveling more and more frequently for work, disappearing for days at a time. When Martha questions him about his frequent absences, he always has a legitimate explanation, but Martha can’t share the feeling that something isn’t right.