Another book in the Cyw a'i ffrindiau series. Plwmp goes for a picnic in the park with his friends, and takes his favourite Swpyr-Deino book with him. But then it starts to rain, and while rushing home, the book falls from his bag. Will Plump, with Jangl's help, be able to find the missing book? And who exactly do they find playing in the back garden of Dewi's house?