Ethan gazed out over Deity’s bow, down the misty-morning canal to Moon’s End. Where was Polly? To get to the tree house they had to go far down the canal, further than the railway tracks. But he had to do it.

The bow deck was cold under his bare feet. He shivered. A pair of moorhens bobbed past Moon’s End and into the mist. He’d got up early to do the work Mum had left for him. She was setting up the market stall this morning and Dad had a little landscaping job in town. They’d driven off in the van, but in two hours Dad would be back. Ethan wasn’t allowed in the dinghy by himself, but it was the only way to get to the tree house and back in time.

Dad had taken two weeks to build the tree house. It had been Ethan’s seventh birthday present. That day, Dad had tied a scarf over Ethan’s eyes. They paddled down the canal for what felt like for ever. “Look,” said Dad as he had lifted off the blindfold. And there it had been.

The tree house was on No Man’s Land. No Man’s Land was a strip of grass beside the canal that didn’t belong to anyone. Dad used to row Ethan there every Saturday, past where the train tracks curved away from the water. They’d tie the dinghy to the big tree, unwind the rope ladder and climb up to the tree house.

Dad would hold the ladder as Ethan climbed. They’d sit on the wooden floor of the tree house and dangle their legs over the side. They’d eat their picnic, looking down at the murky green water and the tourist boats chugging past.

There was nothing to get in the way up there. None of Mum’s boxes to load on the van. No boat chores. Dad would give him the oars on the way back so Ethan could learn how to row. Ethan couldn’t remember the last time they’d been to the tree house. Why had they stopped going there?

Polly was coming down the canal. She was carrying Merlin. She wore her coat with the hood up. She stopped next to the bow plank.

“I can’t wait,” she said. A swirl of mist came out of her mouth.

She stepped on to the plank. It wobbled like always, but she didn’t slow down. She put Merlin on the deck. “I gave her some chicken for breakfast,” she grinned.

Ethan took out the notebook and pencil from the back pocket of his cords. He drew a dinghy, a matchstick boy paddling, a matchstick girl sitting behind.

“We’re taking the dinghy?” Polly’s eyes were dancing.

Ethan nodded. They walked down the bow plank and on to the bank. They went to Deity’s stern and Ethan started to undo the rope that tied the dinghy to a metal ring.

“Where are we going?” asked Polly.

Under the white bridge. Through the stone tunnel. Past the train tracks. To where the ducks are bigger. To my old tree house.

Ethan climbed into the dinghy. He coiled the rope at his feet and picked up the oars. Polly climbed in next to him.

Ethan began to row, past Deity’s stern and east down the canal.

“A proper adventure,” said Polly, her eyes wide. “This is like something out of a storybook. Are you allowed to use the dinghy on your own?”

Ethan shot Polly a look and she knew right away what he meant.

“It’s OK,” she said. “I won’t tell anyone.”

They passed Moon’s End and went under the white bridge. His words weren’t on the blacking any longer. Polly had painted over them.

Drops of water fell on them in the long dark tunnel. They came out into the gloomy light, surging towards the railway tracks. There were no boats to pass down here, no fishermen or walkers. The air smelt like Ethan’s jumpers when they’d been hung inside the boat to dry.

It was further than he’d remembered. They’d been gone twenty minutes. They’d passed the wood and the stone steps that led up to the lane, the overgrown banks and the trees that leant into the water, but they hadn’t even reached the railway line. Ethan felt nervous as they reached the weeping willow tree, but he didn’t know why. It was like something bad had happened under it.

“Ethan, what’s that?” Polly grabbed his oar and drew a sharp breath.

He looked over the left side of the dinghy. A brown lump floated in the water about two metres away. He rowed closer. The lump rolled over. Ethan flinched.

It was a dead dog.

“What happened to it?” asked Polly.

Ethan stopped rowing. He should turn around and row back. They should never have come this far. What if the dead dog was a warning? What if something bad was waiting for them at the tree house? What if there was a horrible boy kicking the tree-house walls and yelling rude words, just like in his nightmare?

“Is it much further?” asked Polly.

Ethan shook his head. He took a big breath. If he didn’t see the tree house in real life, he might never find out what his nightmare meant. He started to row. He had to reach the tree house. He needed to find out what had happened.