The Lunapark circus arrived in town along with a storm of colourful posters, the smell of popcorn and loud music. Tom and Zosia had already been unable to talk about anything else for a week. They wanted to see everything: flying acrobats, clowns juggling cakes and fiery candles swallowed by a grey-bearded magician. But they were most fascinated by Maximus, the world's biggest lion, who could dance on two legs and wear a cylinder on his head. On Wednesday evening, just after lessons, Tom sneaked into Zosia's garden, clutching two entrance tickets found under a school bench. They decided that they would enter the circus tent not only during the performance, but also... at night! "Imagine how many treasures there are!" - whispered Zosia, packing a torch, notebook and cheese sandwiches into her backpack. At midnight, they slipped out of their homes. The circus looked very different when seen in the moonlight. The balloons at the gate were moved by the wind and the colourful flags rustled mysteriously. Suddenly, they both stopped. There was a strange noise coming from the side of the predator cages - quiet murmurs and the rustling of cloth. They came closer, and then their hearts beat harder. The door to Maximus' cage was open wide! Inside lay nothing but a large gold coin embossed with a lion and... a mysterious pawprint shining in the darkness leading deep into the dark acrobats' tent. Tom looked questioningly at Zosia. Should they go in there? What if Maximus had really escaped - or been kidnapped? They took a deep breath, clasping hands, and set off along the mysterious trail....