Day One
When Sirius is thirteen, they get a new House Elf. That's normal. The Black family House Elves get old and feeble, and then there are new heads mounted in the hallway. Then a replacement Elf turns up. This time, though, things are different.

Regulus, ten years old and prone to freaking out, peers at the new creature.

"It's a baby House Elf," he says, sounding overjoyed. "A baby, baby House Elf."

Bollocks, Sirius thinks.

Day Two
"Today, I'll teach Kreacher to swim," Regulus says in a voice of triumph.

"Right, because teaching him to ride a broom went so well," Sirius says.

"Swim," Regulus continues dreamily, "and then sew. And then blow stuff up."

Sirius bangs his head on his headboard, rather harder than he meant to. "If you must."

"You taught me how to do all that, so why shouldn't I teach Kreacher?" Regulus scrumples his face into what he knows is an adorable expression.

Sirius is sure he wasn't that sneaky when he was a little kid. He tries not to grind his teeth. "Yeah, but you're my little brother."

"And Kreacher's my little brother!"

Sirius shakes his head, but he doesn't say anything, because hey, why not? Regulus needs someone to play with while Sirius is away at Hogwarts, and it's still a while before Regulus goes. Sirius cringes inwardly when he imagines Regulus trying to bring Kreacher with him, rather than a cat or an owl.

He decides that this is the longest summer ever.

Day Three
"Bella," Regulus says seriously, "You're always breaking my toys. Don't break my House Elf. He's my best friend, besides Cissy, Dromeda, Sirius, and you."

Bellatrix, who has been visiting for what promises to be the world's longest week, sighs dramatically. "I just think you shouldn't be carrying on that way with a slave."

"Am not," Regulus says. "I'm carrying on with Kreacher."

Sirius rolls his eyes and thinks it's weird, but hey, his friends aren't exactly normal. If Regulus wants to be best friends with a House Elf, that's his business. Bellatrix shouldn't have tried to step on Kreacher.

And ok, Regulus himself has tried to blow Kreacher up numerous times, but that was all done with love. Regulus is interested in explosives. Sirius can sympathize. Bellatrix is just an evil person. The fact remains, however, that in this case she's on Sirius' side.

She looks like he feels. "Regulus, darling," she says very patiently, "You're a precious, wonderful, brilliant child," (Sirius sees the doubt in her eyes on brilliant) "but you just can't be friends with that."

"Ok," Regulus says. And he goes back to trying to put a doll's dress on Kreacher.

Bella looks at Sirius, but she seems far from defeated. "I have a plan," she tells him.

Day Four

Regulus can be really loud when he wants to.

Sirius is enjoying himself, frankly. Even if he hates Bellatrix and everything she stands for, and her mom, and her face, he can still enjoy a harmless kidnapping spree. He ties the top the sack in a tighter knot and peers out from behind the house where they're hiding.

Regulus is stomping around square angrily, looking ready to put explosives in someone's bed. Again.

Bellatrix holds a finger to her lips. "Try to keep that creature quiet."

Sirius clamps down tighter on the sack and reflects on what an appropriate name Kreacher is. Oh well, at least their plan is working.

Then Regulus goes and gets Bellatrix's sisters.

"Fuck," Bellatrix says happily.

Sirius grins at her. Ok, they can both enjoy a challenge.

Andromeda and Narcissa are listening earnestly to Regulus' tale of woe. And cooing over him. Regulus frowns around the yard. "He was just here. Do you think he ran away from me? Why would he do that?"

"Oh, Regs," Narcissa says, making appropriately woeful eyes.

Bellatrix stares at Narcissa in horror, and Sirius pretends to gag.

Andromeda shakes her head. "He wouldn't run away. That Elf loves you, although I'm sure I don't know why."

"I don't try to blow him up much," Regulus says, sniffling.

"Erm, right," Andromeda says skeptically.

"He's all alone in London," Regulus says, looking ready to burst into tears.

Sirius quirks the corner of his mouth at Bella. "Feel bad," he says.

"Mm," she says, perhaps in agreement.

Sirius doesn't get a chance to find out. There's an explosive crack, and suddenly the bag Sirius is holding is a lot lighter.

Sirius sees Kreacher sprinting across the square–in full view of the Muggles–and Regulus' face lighting up.

Kreacher throws himself at Regulus. "Kreacher missed Master Regulus sooooooo much he could barely stand it!"

"Oh, Kreacher," Regulus says tearfully. "You, too."

Day Five
After the Muggles' memories have been modified, Regulus is forced to play with Kreacher inside, at least for a while. He casts occasional dark glances at Sirius and Bella, but most of the time he's too occupied with teaching Kreacher new skills.

Sirius is lying in the middle of his bedroom floor, despairing of life. Bellatrix is perched on the bed, reading a magazine and intermittently insulting Sirius' taste in music.

"Hey," she says suddenly.

Sirius perks up. Something to do?

"Let's drown it," Bellatrix says.

Again with the sack. Sirius doesn't want to waste any time, and he and Bella are both still considerably shaken by yesterday's disapparation incident.

Bellatrix does the deed, chucking the sack as far as she can into the river. "Right," she says, "There's that taken care of."

Sirius punches her awkwardly in the arm as the walk back up the hill and into the back yard of Number Twelve.

Where Regulus is listening earnestly to a sopping wet Kreacher.

"Fuck," Sirius says.

Day Six
"Where did you get this stuff, anyway?" Bellatrix asks, frowning down at the sticks of dynamite.

"Oh," Sirius says breezily, "I bought it in London." The truth is, he nicked it from James, who apparently stole it from a Muggle shop.

Bella wrinkles her nose. "It looks Muggle."

"So does your face," Sirius says.

It's a bad plan. It turns out that getting a House Elf to hold still in order to tie dynamite to its feet is even harder than it sounds in theory. Kreacher kicks, bites, flails, and yells for Regulus.

Regulus appears within seconds, frowning slightly at Sirius. "You leave that to me," he says, grabbing the dynamite and the Elf.

Sirius shrugs as Regulus departs. "Hey, at least he doesn't hold a grudge."

"No," Bella says, "But Kreacher might."

As it turns out, Kreacher does. At least, that would explain the snakes in Bellatrix and Sirius' beds that night.

Day Seven
Sirius and Bellatrix give up. Kidnapping, drowning, and explosives. Nothing works. They sit on the steps of Sirius' house, defeated.

Regulus was playing in the square, but he comes running back to the house just as Sirius and Bella are giving in to despair. "Guess what?" he says.

"Kreacher was shot by a passing Muggle?" Bellatrix asks without hope.

"Nope," Regulus says, "I taught him how to ride my bike."