Maigret's Doubts by Georges Simenon

Xavier Manto, a mild-mannered toy salesman from a Paris department store, has come to confide his secret fears to Inspector Maigret: he suspects his wife is plotting to poison him. Then when Maigret receives a visit from Madame Manton on the same day, he is not sure who to trust. Soon he becomes caught up in a treacherous feud between husband and wife, where nothing is as clear cut as it seems.

Translated by Shaun Whiteside