Lexie Moon built her latest invention, The Vocabuliser, to help people learn to say tricky words, like spaghetti and Worcestershire. She secretly tests it on her little sister with amazing results. But the device is stolen by infamous gadget thief, Gizmo Lightfinger, who sees other people's inventions as his ticket to glory. Out for revenge on the Inventors' Guild after a lifetime ban, Gizmo goes on a gadget stealing spree across town. With Grandad's help, Lexie devises a plan to catch the gadget thief and get her invention back. The pair use hers Nose-Knows sniffer tracker device to follow Gizmo's trail and along the way they meet several more victims-all with something in common ...The trail soon leads them to the thief, who has attached a stolen power booster to The Vocabuliser and renamed it The Word Grabber 9000! An unknown glitch in Lexie's original design has transformed it into a device that steals people's words-all of them-the exact opposite of what Lexie intended! Determined to bring Gizmo to justice before he can cause anyone else to lose their speech-or claim her invention as his own-Lexie sets out with Grandad to stop the thief in his tracks. But when Grandad is zapped into silence, there is just one thing left to do! And when The Vocabuliser starts to creak and groan, Lexie knows her plan is well on track ... although that little glitch might have one more surprise in store!