They flew through the door and landed with a splash. Pip opened his eyes then stared.

A stripy  blue fish stared back, blowing bubbles.

He tried to speak, but something was in his mouth. It was a snorkel, attached to an oxygen tank strapped to his back. That’s how he could breathe underwater!

Zena swam beside him, pointing below. The seabed was a bright landscape of shining rocks, coral and shimmering fish. He grinned, but she shook her head and kept on pointing.

He looked down again. Finally, he saw it; another word spelled out in pebbles in the sand!

World.

Quickly, he pieced the words together. Tell the world. What did it mean?

Pip shivered. Why was he swimming in a shadow all of a sudden? He looked up. There was a big, long shape swimming above him, its surface grey and as smooth as a stone. The big, long thing had a sharp, pointy tail and very sharp, pointy teeth!

“Shark!” he shouted, nearly spitting out his snorkel. Zena started to swim . She’d seen the shark too. They swam as fast as they could. The shark glided above, following them.

Ahead, something small was moving through the water. It was Libro, driving a little cat-sized submarine! Sure enough, the sneaky cat was heading towards another door on the ocean floor.

Quickly, they swam towards him. But before they could get there, he vanished through it.

We need to hurry! They both thought, hurrying their pace. Finally, they made it through the door, tumbling through in a gush of foamy water. They landed on hard, cold ground. They turned around and yelped with horror. The shark had swum through too and was lying on the floor, close to where they stood.

Pip looked at Zena. Zena looked at Pip. What were they going to do?