When a thief breaks into the boarding house and steals the rare and valuable feathered mask belonging to Professor Tobin, Maisie realises she has a new mystery on her hands.

Maisie Hitchins longs to be a detective. She’s sure there are lots of adventures to be had on the streets of Victorian London. And, together with her faithful puppy, Eddie, she is determined to follow even the slightest scent of a mystery - no matter what!