We were asked to write a story set on a beach. We had to pay particular attention to the setting.

This story is sort of autobiographical. When I was about the same age as Henry I went treasure hunting in the fields near the house where I lived. And I found real treasure! The same treasure that Henry finds...

The beach was yellow and featureless. The sea mumbled at it with gentle blue wavelets. Here and there brown patches of seaweed provided shelter for small lurking crabs. In the distance someone was galloping a horse along the firm, wet sand at the edge of the sea. Henry, who was nine years old, watched the horse until it was out of sight. "Wow!" he said at last, "there's so much sand here. We can make a huge sand castle with all this to use up."

"But what about the buried treasure?" asked William, who was eleven and who therefore found sand castles boring. "If I was a pirate this beach is exactly where I'd bury my treasure. So it must be here somewhere. Stands to reason. All we've got to do is dig for it."

"But how will we know where to dig?" asked Henry, intrigued by the notion of treasure. "It's a big beach. You can't find buried treasure unless you've got a treasure map. And it's got to have an X on it. It's not a proper treasure map if it doesn't have an X on it."

William found this logic very convincing. "OK," he said agreeably. "First thing we need to do is make a treasure map. You can put the X on it." Henry's eyes lit up. That sounded exciting.

They walked back to the caravan that their father had hired for the holiday. "Dad," said William, "we need a treasure map for the beach."

Their father looked up from the fishing rod he was assembling. "A treasure map?" he said. "I know just the thing." He rummaged around in a drawer that he pulled from under one of the beds. "I'm sure I saw it in here..." he muttered under his breath. Then he gave a cry of triumph and produced a pad of paper and a box of crayons. "There you are," he said. "Just what you need for a treasure map."

William tore off a piece of paper and spread it out on the table. He drew a line across it. Then, forehead furrowed in concentration, he used a yellow crayon to fill in the bottom half of the paper. "This is the beach," he explained to Henry. He gave Henry a blue crayon. "Use this one to colour in the sea," he said. Henry dutifully turned the rest of the paper blue.

When they were finished, they looked at their map with great satisfaction. The scribbled yellow area looked just like the real beach and the big blue bit looked just like the real sea. "That's a proper map," said William. "It's got everything important on it."

"No it hasn't," said Henry. "There were all those brown blobs of seaweed as well."

"Oh yes," said William. "So there were." He picked up a brown crayon and scribbled some brown bits on the beach. "There," he said, deeply satisfied. "Now all it needs is an X."

Henry picked up a red crayon and carefully drew a big X in the bottom left hand corner of the beach. "That's where the treasure is," he said. He and William picked up their spades. "Dad," he said, "we're off to dig up the treasure."

"OK," said their father. "Make sure you're back in time for tea."

The beach hadn't changed while they'd been gone, though the horse rider had reappeared, trotting this time rather than galloping. Maybe the horse was tired. Henry and William compared the beach to the map they were carrying. The two matched up very well. "Look," said Henry, "those two patches of seaweed are just like these two on the map. So the treasure must be just here." He scraped a big X in the sand with his spade. "And here's the X," he said. "Let's dig."

William folded the treasure map carefully and put it in his pocket. Then he picked up his spade and joined the enthusiastically shovelling Henry. Sand flew hither and yon. Much of it trickled down William's neck, itching and scratching simultaneously – a very odd feeling.

The hole got deeper and deeper. Then Henry's spade clanged against something solid and he gave a triumphant cry. "I've found the treasure!"  He threw down his spade and began to feel around in the hole. William leaned on his own spade and watched Henry's hands exploring the sand. Then Henry lifted something out of the hole. "It's gold!" he gasped. "Real pirate gold. Look!"

William looked. Henry was holding a glittering, gleaming object that reflected the sunshine in dazzling sparkles. "It's a golden dog's head," Henry said excitedly.

"Let me look at it," demanded William. A little reluctantly, Henry passed it to him. William examined it closely. It was a flat, two-dimensional representation of the head of a German Shepherd, delicately fashioned so that almost every hair could be distinguished. A huge tongue protruded from its mouth. Its ears were erect and it was panting with eagerness, clearly about to chase something. Sand was compacted in the hollows of the piece. "Let's take it down to the sea and wash the sand off it," said William.

With the sand removed, the dog's head was a soft, golden shimmer in the light from the setting sun. William gave it back to Henry and said, "We should take it back to the caravan and show it to dad."

"Real pirate gold," said Henry as they walked. His eyes were round with wonder. "Real pirate gold."

Their father was very impressed with the pirate gold and he congratulated Henry on his find. But when Henry wasn't looking, he winked at William and put his finger to his lips in a shushing gesture which made William suspect that there was more to this pirate treasure than met the eye. But, obediently, he kept quiet about it for the moment.

Henry refused to be parted from his treasure trove. It sat beside his plate at tea time as they ate the fish their father had caught that day, and it slept beneath his pillow when he went to bed. William, being two years older, was allowed to stay up for an extra hour. When he felt that Henry was safely asleep he said, "Dad, it's not really gold, is it? That's why you told me to keep quiet."

His father shook his head. "No it isn't," he said. "It's a horse brass, an ornament used to decorate a horse's bridle on special occasions. It's a very beautiful example of a horse brass, but no, it isn't gold and it isn't worth very much."

William remembered the horse they'd seen galloping and trotting on the beach and he remembered the ecstatic look on Henry's face when he found the pirate treasure. He was fond of his little brother and enjoyed seeing him happy. "Let's not tell Henry that, eh dad?" he said.

His father smiled and ruffled William's hair. "No," he agreed. "Let's not."