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! On a visit to the British Museum, Maisie meets Professor Tobin's old university acquaintance Lord Dacre, who's devastated about the recent theft of one of his most prized possessions – an Egyptian scarab beetle made of gold and encrusted with jewels. It's not long before the lost artefact turns up on the muddy bank of the river Thames, but its missing its precious ruby eyes. When the wrong man is convicted of the robbery, it's up to Maisie to find out who the real scarab stealer is.