When Amelia and her friends are invited to Florence's grandmother 350th birthday party, they are very excited! Grand-yeti Clemence lives in the Yeti Pits, a maze of candle-lit tunnels and caves carved into Yeti Mountain. But not long after arriving, the precious glittery treasures of the ancient yetis start to go missing. And when Tangine goes missing too he becomes the prime suspect! Not only that but the tunnels of Yeti Mountain have started to collapse on themselves and it looks like Florence and her family will have to move far away. It's looking like the gang might never see each other again! Will Amelia be able to solve the mystery of the missing yeti treasure? And will she and her friends survive the perils of the crumbling Yeti Mountain and all the booby traps on the way?