Agent Amelia: Ghost Diamond!

These are the secret agent case files of Amelia Kidd. She's saved the world loads of times from evil geniuses and criminal masterminds, thanks to her great disguises, her own gadgets (which sometimes work), and her brilliance at improvising in sticky situations.

The three stories are:
The Case of the Ghost Diamond, in which Amelia foils a daring jewel theft during a class trip to the museum, thanks to her convincing granny disguise, and her mirror-on-a-stick gadget.
The Case of the Cat Nappers, in which Amelia discovers the amazing reason for all the disappearing cats in her area - they have all been trained to become burglars! Cat burglars! Luckily Amelia's quick thinking foils the robbery and catches the thieves!
The Case of the Whispering Weeds, in which an innocent trip to the Garden Centre results in Amelia having to use a runaway trolley to escape from an evil genius who has cultivated a weed army to control every crop on the planet. But naturally, Amelia bounces back and trounces the madman. What a good job that Garden Centres also sell weed killer!