“Listen to this, Dolf,” said Henry Hunter. Reluctantly I tore myself away from Deathdealers 4: the Horde, which had been taking all my attention for the past hour. It was sports day at St Grimbold’s School for Extraordinary Boys and, since neither Henry nor I much cared for three-legged races or the ten-metre dash, we were both hiding out in Henry’s rooms.

I was surprised to see that HH wasn’t about to quote me something from a book. Instead, he was holding a sheet of very thin paper, on which was written several lines in rather shaky-looking handwriting. Thinking that only Henry could know people who still wrote letters rather than sent emails, I gave him my full attention.

Once he was sure he had captured my interest, he began reading.

“Sounds a bit mad to me,” I said. “Who is Charlie anyway? And what’s a… spinnaker?”

“Charlie Stevens is an old friend,” answered Henry. “His parents knew mine before we were even born. And it sounds like the Spinnaker is a boat, from the way Charlie writes about it. His parents were always talking about sailing off somewhere in search of buried treasure and stuff.”

“Buried treasure!”

“Well, Timothy – that’s Charlie’s dad – fancied himself an expert on pirates. He once told me he knew where Captain Morgan had hidden his loot.”

“Who?” I asked.

“Captain Morgan was one of the greatest privateers of all time,” said Henry. “He started out as a pirate and ended up as the governor of Jamaica. Then he either lost or hid all his money and lived out his last days telling stories in return for jugs of ale.”

I raised my eyebrows. Captain Morgan sounded like quite a character. “What’s a privateer?”

“A kind of licensed pirate,” said Henry. “Kings and queens used to give a letter of marque – that’s like a licence – to unscrupulous captains to go off and raid enemy ships. Then they’d bring back all sorts of treasure to fill the royal coffers.”

As usual Henry was going into way too much detail, and I wasn’t sure of his point. “So what does all of this have to do with your friend Charlie?”

“No idea,” said Henry, smiling. “But I plan to find out.”

We didn’t have to wait long. That afternoon, a car arrived to pick us up and drive us into the wilds of the country. Having two millionaire uncles as guardians meant that Henry could call up a car – or even a private jet – at a moment’s notice.

We drove from St Grim’s in Sussex into deepest Oxfordshire, to the small town of Thame. There, we took a wandering single-track lane that wound away from the main road and ended up at a pair of big iron gates. A small camera mounted on a gatepost swivelled down to look at us, and moments later the gates swung silently open. We proceeded up a tree-lined drive to a big crumbling house with long, narrow windows. To one side of the solid wooden front door stood a huge statue of a raven carved out of smooth dark stone. On the other side was an even bigger and weirder creature that Henry explained was a griffin – half eagle and half lion. To be honest I found both statues a bit creepy, but Henry said they were carved by a famous sculptor. I wondered if that was meant to make me feel better about them. It didn’t.

As we came up to the door, two huge Irish wolfhounds came bounding towards us. I know a bit about dogs from my aunt, who used to keep a poodle, but this was something else entirely. As the car stopped they stuck their faces up against the windows and barked. I flinched, thinking I’d rather be in a three-legged race at St Grim’s than chewed up by one of these things – they were easily a metre tall and looked pretty fierce. But as Henry calmly opened the door they suddenly became extremely friendly and began giving him a good licking.

When I got out gingerly behind him, they repeated this kindness for me (on the whole I preferred the time I had to take a bath in a rusty wheelbarrow, but that’s another adventure…)

“Can you wait?” Henry asked the driver. “If you go around to the side of the house you’ll be able to get a cup of tea from the staff.” (Yes, I know, ‘staff’. I told you Henry knows some pretty posh people.)

The driver nodded and we approached the big front door. Henry rang the bell – it was the old-fashioned kind where you pull a rusty handle and can just hear as it rings somewhere in the depths of the house.

It was several minutes before the door opened. Facing us was a tall, heavy-browed man with a big moustache. He glared at us.

“Well. What do you want?” he demanded.

Henry flashed him his best smile. “It’s Henry Hunter, Mr Bligh. This is my friend, Adolphus Pringle. We’ve come to see Charlie.”

“What? Oh, yes, Hunter…” said the man, frowning.

“We were sorry to hear about Mr and Mrs Stevens,” said Henry.

The man’s face softened a bit. “Yes. Bad business. Charles is still very upset. I’m not sure he wants to see anyone.”

“I’m sure we can cheer him up,” Henry answered. “Better than just moping about, don’t you think?”

“I suppose you’d better come in then,” the man said. “He’s upstairs in his room, I imagine.”

Henry nodded and I followed him in. The house was even more impressive inside. The hall was huge with lots of old paintings hung on the walls of men and women who looked as if they had been forced to stand still too long. (One of the portraits even included two big dogs that looked a lot like the wolfhounds.) A long, curving flight of stairs led upwards to a landing off which several doors could be seen.

Henry made his way straight up the stairs to one of the doors and knocked.

It literally flew open and a tall, gangly boy with a shock of curly red hair and an enormous number of freckles grabbed Henry by the arm and pulled him inside. As I followed he stared at me suspiciously.

“This is Dolf,” said Henry. “You can trust him.”

“You didn’t say anything to Jack?” Charlie asked anxiously. I deduced that the sour-faced man downstairs was Charlie’s uncle.

“Not a word,” answered Henry.

Charlie’s room was large and airy, with a big window. I didn’t need to be a genius like HH to work out what he was interested in. On every surface, including the floor, were model boats. Some were the small kind you can sail on ponds; others were large and graceful and looked like they should be in a museum. Most of them were old-fashioned – galleons, Henry told me later – with sails and ropes and masts sticking out everywhere. On the wall hung a photograph of a very modern, white, sleek boat, like the something from a James Bond film. ‘Spinnaker’ was painted on the side in big black letters, and on the deck stood three people – Charlie, easily identifiable by his wild red hair, and two adults who I guessed were his parents. They all looked happy and carefree.

This must the boat from which Charlie thought he had seen a ghost ship.

Henry examined the photo for a moment. Then he turned to Charlie. “So, tell us what happened.”

Charlie sat down on the bed and stared at us glumly. “I’m not sure where to begin,” he said slowly.

“Beginning at the beginning always works for me,” grinned Henry, pulling up a spindly-looking chair and dropping into it. I hunkered down on the wooden floor and found a rather squashed but perfectly edible bar of chocolate in my jacket pocket. Together we listened to Charlie Stevens’ strange and scary tale.