Reunited with Tinker, who featured in an earlier adventure: the Famous Five are invited to camp out in a field close to his house (in which Professor Hayling, Tinker’s father who is a scientist lives). When a Circus arrives, and sets up camp, close by – the Famous Five are contented with the mild excitement of watching the Circus folk’s antics, and getting to know them, but then – real commotion strikes, when a tower in the grounds of Professor Hayling’s house – is robbed. Can the Five track down the culprit? And what has the mystery got to do with Kirrin Island?