When Yosser's best friend, Kylie, comes back from Thrill City she is full of amazing stories about the best ride there - Sita, Snake-Queen of Speed. Yosser knows that she MUST go on the ride but there is no way Dad will pay for such an expensive day-trip. Her only chance is to earn enough money to go. But how? An opportunity presents itself when Kylie's dad's prize ferret, Thunderball Silver the Third, mysteriously goes missing just days before the Grand Ferret Championships. Yosser and Kylie must find a way to catch Thunderball (and the thief!) and make enough money to make their dream come true.

Illustrated by: Helen Bate