With the school term over and summer in full swing, Margery and Clementine Butcher-Baker decide to make the most of their vacation period by setting off for the charming village of St-Martins-on-the-Water. Their plan is to explore the scenic locale and enjoy some restful days before the whirlwind of Mrs. Smith’s upcoming hen do. Unfortunately, their tranquil getaway takes a sinister turn on their very first night.

Tragedy strikes when the local mayor is found dead on the floor of the hotel restaurant, a victim of poisoning. The villagers are convinced that “The Poisoner,” a notorious figure from the past, has returned to wreak havoc once again.

As suspicion falls on Margery and Clementine, they find themselves ostracized by the wary residents. Perplexed and hurt, they’re puzzled by unanswered questions. Why are the villagers so quick to believe the worst about them, especially Clementine?

And as more people in the village fall ill, the chilling question remains: is it the work of the infamous Poisoner, or is there a new, sinister presence at play? Will the mysterious killer strike again, and can Margery and Clementine uncover the truth before it’s too late?