Chapter One: In Which Kreacher Is Summoned
"He couldn't have left, could he?" said Harry. "I mean, when you said 'out,' maybe he thought you meant, get out of the house?"
"No, no house elves can't leave the house unless they're given clothes, they're tied to the family's house," said Sirius.
"They can leave the house if they really want to," Harry contradicted him. "Dobby did, he left the Malfoys' to give me warnings three years ago. He had to punish himself afterwards, but he still managed it."
Sirius looked slightly disconcerted for a moment, then said, "I'll look for him later-"
"Are you a wizard or what, Sirius? Use magic or something!" said Harry, exasperated.
"Er, right. I can just call him. Kreacher!"
Kreacher the house elf appeared with a loud crack of displaced air. "Yes, Master?"
Harry looked pointedly at Sirius, who immediately understood.
"I command you to tell me truthfully what you were doing before you were summoned!"
Kreacher said, unpleasantly, "Bad Master wants Kreacher to tell what Kreacher was doing. Kreacher was with Miss Cissy and Bella. They are kind to Kreacher, so Kreacher told them what they wanted to know!" He muttered some more, referencing himself in the third person every now and then.
"Who are Cissy and Bella, Sirius?" asked Harry.
"They are my cousins, Narcissa and Bellatrix."
"They wouldn't happen to be Narcissa Malfoy and Bellatrix Lestrange, would they?" said Harry, half hoping he would say no.
"I'm afraid so," said Sirius grimly. "I'm going to have to call Dumbledore."
"Hang on. Before you do that, would you mind ordering Kreacher to follow my orders?"
"Sure. Kreacher!"
Kreacher stopped muttering. He looked up at Sirius, "Master?"
"I command you to follow all of Harry Potter's commands!"
Kreacher grumbled, "Yes, Master. Blood traitors and Mudbloods in the house of Black, mistress would be very angry with Kreacher."
Sirius took off to find Dumbledore. Harry said, "Stop talking and moving, Kreacher!"
Kreacher obeyed reluctantly.
"Listen carefully. You are to forget everything that happened in 1995."
It worked. Apparently, Memory Charming a house-elf was really simple.
Kreacher had forgotten the Secret too, and was looking around, confused. The Fidelius apparently behaved weirdly in such situations.
Harry took the confused elf out of the house. He ordered him to forget everything that he had ever known, and to start a new life somewhere else disguised as a Muggle.
AN: Why did Sirius not call Kreacher? Why did he say 'I'll look for him later'? Is he not a wizard? Obviously he is, so he must be out of practice or something. Whatever works.
Really stupid of Sirius not to command him to appear.