Pranksters Frankie Fish and Drew Bird have got hold of Grandad's time machine, but it's no laughing matter. Grandad and Nanna have disappeared to 17th century China, and it's up to Frankie and Drew to save them! With the help of a mysterious new friend, the boys must overcome armed guards, giant dragons and one GIANT wall to get to the Emperor's secret prison. But even if they can get inside, how will they break Grandad and Nanna out and get them home again?