This is one of Georges Simenon's noir novels (or, "romans durs," as he called them), in which a hardworking widow hires a killer just out of prison as a handyman. Their relationship quickly turns into something else, until he starts to fall for the girl next door. And then things really go downhill from there.
While I love Simenon's Inspector Maigret mysteries, his noir novels are definitely his best work. The Widow is short, but powerful and dark. I definitely need to check out more of these.