Matilda loves science and inventing. Her heroes are Marie Curie, Leonardo da Vinci and Thomas Edison, and one day she wants to be a famous inventor herself.

So when she doesn't win the school science fair, she's devastated - especially as the judges didn't believe she'd come up with her entry on her own.

When Matilda shares her woes with her Grandma Joss, she's astonished to learn her grandma was once a scientist herself - an astrophysicist, who discovered her very own planet.

Trouble is, Grandma Joss was also overlooked - her boss, Professor Smocks, stole her discovery for himself. And he's about to be presented with a Nobel Prize. Matilda concocts a plan. They'll crash the award ceremony and tell everyone the truth!

So begins a race against time on a journey through Paris, Hamburg and Stockholm, and on which they encounter a famous film star, a circus, and a wanted diamond thief!