Meet Frankie Potts, the village of Tring's number one girl detective. She has flaming red hair, a questioning mind and an addiction to gobstoppers. And she is REALLY good at solving mysteries.When Frankie is adopted by a dog at the window of her favourite sweetshop, there's detecting to be done.The dog, Sparkplug, is adorable. Even Frankie's formidable Grandma M goes all soft and goopy in his presence. Sparkplug can ride a skateboard like a pro, high-five, dance on his hind legs and sniff out a mystery two houses away. He's the ideal dog for a detective. Sparkplug wants to stay with Frankie, and Frankie would dearly love to keep him - but where is he from?There are other mysteries to solve, and they all seem to be linked: trails of ants; Grandma M's odd behaviour; her secret tattoo . . . What? When and WHY did cardy-wearing Grandma get a tattoo?A circus has just arrived in the village - it seems a good place to start looking for clues. But first, Frankie will have to get Sparkplug past Tring Dog Control and her arch-enemy, Ralph Peter-McGee.