Inspired by a drawing by saintlilith, combined with some encouraging reactions on The dawn of a pirate's life.
Thanks to Jlocked for proofreading and the title.
Not a second after John's mother had pressed the bell, the door swung open to show a very excited Sherlock.
"John, John, John, John, John, John, John! Come on, you have to come look, why are you so late, come on!" The small boy grabbed John's hand and dragged him along, leaving Mrs Watson in the door opening, laughing at so much enthusiasm.
In their haste, the boys almost kicked over the large, silver umbrella stand by the door, but then they were out of the long corridor in the blink of an eye.
"What... What's going on?" John asked, a little breathless. He had not even had the chance to say hi to Sherlock. And as far as he knew, they had actually been early, rather than late, as he had already asked his mother if they could leave three times before they actually did.
But Sherlock didn't answer and ran into the living room, which was large, filled with leather chairs and a long sofa, and light thanks to the big windows looking out on the garden.
There, Sherlock finally stopped and waved an arm. "John, this is Redbeard. Redbeard, this is John," he said, almost jumping with excitement.
A small, real, living dog with reddish brown hair stood up in his basket and eyed John curiously.
John could only stare. "Is he... is he yours?"
"Obviously!" Sherlock beamed. "He is my new friend."
"Wow..." John said, stepping closer. At first, he felt a little shy, but then he kneeled and started petting the dog.
"He likes you!" Sherlock said, joining John in his attention to Redbeard. "Good."
He grinned at his mother as she entered the room.
"Oh," John's mother said, looking surprised and lingering a little behind Mrs Holmes. "That explains why Sherlock was so happy! Great news, indeed."
"Don't worry," Mrs Holmes smiled at her. "Redbeard is a really good dog."
"Oh, I'm sure he is," Mrs Watson said a little nervously. "I've just never liked dogs. Even though he's a puppy... I'd rather keep my distance." She was clearly trying, and not quite managing, to relax.
"Of course," Sherlock's mother said, putting a gentle hand on her shoulder. "I'll just make you a cup of coffee. Boys, you can take Redbeard out, but behave. If you need us, you can find us in the kitchen."
John hugged Redbeard, who clearly didn't mind at all. "Shame Mum doesn't like dogs," he sighed. "He's brilliant!"
"I know," Sherlock said. "But don't worry. You can come play with us anytime."
"Thanks," John grinned.
"Let's go outside. Redbeard can do loads of tricks," Sherlock said.
It turned out that that was a little exaggerated, but the young dog was learning. For some time, the boys ran around in the garden, chasing an elated Redbeard and making him fetch a ball. Hide-and-seek, however, didn't quite appear to be his forte. Rolling over every time, it looked more like he wanted to be found for a belly-rub, which defied the purpose of the game a little. Soon, Sherlock and John gave up and went back to throwing the ball.
Eventually, all three of them were getting rather tired of running.
"I really can't wait until he can help me with my experiments," Sherlock said, when they had sat down at the large, oval kitchen table for a glass of lemonade and a piece of cake. "Then he can bring me my equipment. Maybe even test some things. Nothing dangerous, of course," he added as he saw John's face.
"You're so lucky," John said, scratching Redbeard behind the ears and looking genuinely happy for Sherlock.
...
"Come on," Sherlock said as soon as the last crumb of cake had disappeared. "I'll show you my room." It was something the children in the books he read always did when they had friends over, so he had been waiting for the opportunity. Feeling proud, he went up the stairs before John.
"Wow, it's amazing!" the older boy said as soon as Sherlock opened the door.
The room was rather large and filled with a chaotic clutter of toys. A few stuffed animals were sitting on a shelf, some of them in rather bad postoperative shape. The bed, however, was made up neatly, with red sheets adorned with little black bicorn hats, ships and skulls. In the middle of it lay a big cuddly hedgehog, which was a little flat on one side, where Sherlock always lay on top of it. In a corner, there stood a small army of tin soldiers, next to a large bookcase. Against the other wall, there was a table carrying a chemistry set.
"Wow," John said as he saw it. "Mum would never let me play with that."
"We can do some experiments later," Sherlock suggested, grinning widely at John's admiration of the room. "But I have another plan for now. Look..."
He dived into his wardrobe, rummaged around and then pulled out a black cloth. John's mouth fell open as Sherlock unrolled it.
"That's a real pirate flag!"
Sherlock nodded. "The Jolly Roger," he said solemnly.
John frowned for a moment, then pointed at the skull. "So that's Roger? He doesn't look very jolly..."
"I... I... I guess," Sherlock answered, staring at John. He clearly had never thought of that before.
"But it's amazing," John said quickly. "Skulls are cool!"
Sherlock nodded, very convinced. "I got it from Mycroft," he said, still holding up the flag, sounding as if he was admitting something unpleasant.
"Oh, that's great! Even if my sister was older, I don't think she'd ever buy me such a good gift," John said, wrinkling his nose. "She only likes pink things!"
"Ew," Sherlock said, resulting in a bout of fierce nodding from John.
"Where is Mycroft, actually?" he asked.
Sherlock's expression grew dark. "Away. But it's fine. I have Redbeard now and he is a lot more fun." Then a mischievous twinkle appeared in his eyes. "We could pick his lock and go explore in his room..."
"Nah," John said, looking at the pirate flag. "I think we have to go play pirates."
Sherlock smiled widely and threw him an eye patch. Then he grabbed John's hand to pull him along, holding the flag in his other hand. "Come on, then!"
...
Running out in the fields surrounding the house, the two young captains managed rather easily to retrieve treasure after treasure from their tail-wagging enemy. When they returned inside, it was already getting dark.
"This was really a fantastic day," John said, hugging Redbeard one last time, before his mother helped him into his jacket, at safe distance from the dog. "Thank you for having me, Mrs Holmes."
Sherlock's mother smiled at his politeness. "You're always welcome."
"Thanks! And thank you for all the fun, Sherlock." John pulled the smaller boy into a strong hug. "You're my best friend."
When he let go, Sherlock was still staring at him, blinking rapidly. He didn't say another word until a long while after John and his mother had left, but that was fine. John knew.