Autumn has arrived, with crisp, cold mornings, dew on the grass and hedgerows full of blackberries. Budding garden sleuth Poppy is excited when she's invited to a party in a beautiful orangery and the last thing she expects is for the glamorous evening to end with a lethal wasp attack! But the tragic death turns out to be no accident and Poppy is horrified when Joe Fabbri, local handyman and her mentor and friend, becomes the main suspect in a murder investigation. Determined to prove Joe's innocence, Poppy sets out to solve the case—with help from her neighbour, 'mad scientist' Bertie and his new robotic invention, not to mention a particularly stinky mushroom!

Meanwhile, with the coming of cold weather, Poppy is discovering that gardening isn't just sunshine and roses. As she grapples with wind and rain, and unpleasant autumn chores, she wonders if she's bitten off more than she can chew. With no horticultural experience and a long winter ahead of her, can she really make a success of the cottage garden nursery that she's inherited?

As Oren, the talkative ginger cat, lends a paw, and crime author Nick Forrest helps her dig for clues, Poppy makes a startling discovery: could there be a link between the murder victim and the long-lost father she has been trying to find? Would solving this case also give her answers to the biggest mystery from her past?