Kreacher was alone. No one lived at Grimmauld place any more, unless you counted the various magical creatures that now infested this place. Oh, if only his mistress would see the state in which the house was now. He would have to punish himself most severely, but she wasn't there. No one was there. Only old Kreacher.

Kreacher was stuck in this house, waiting for his master, who would not return. Sentenced to lifelong imprisonment in Azkaban. But as long as he lived, Kreacher was bound to stay at Grimmauld Place, unable to go to Narcissa at Malfoy Manor. She would be a proper mistress, unlike Master Sirius who had run away.

But as long as Sirius lived, Kreacher would stay at Grimmauld Place, trying to find a way to fulfill the task that Master Regulus had left him.

Poor Master Regulus. How Kreacher wished he was still alive. No other wizard had ever treated him as kindly as Regulus. Mistress Walburga had always been strict with Kreacher. He had to punish himself for the smallest mistakes. But Regulus had been almost a friend. Kreacher had been Regulus' servant, but Regulus had always treated him with respect. Something no other wizard had ever done, not even Sirius, who hated Kreacher like he hated everything at Grimmauld Place.

And then that fateful night had happened. Master Regulus had been so proud. Proud that he, the youngest Death Eater, could help the Dark Lord. The Dark Lord had taken Kreacher to the sea, into a dark cave. And there he had to drink that most horrible potion.

Every gulp had felt like all water was drained from his small body, and it made him relive his worst memory. The day Marius had to leave. The day Walburga beheaded the Blacks' oldest house elf. The day young Master Sirius ran away.

And then, the Dark Lord placed a locket at the bottom and then poured new potion into the basin, and left Kreacher alone. Alone on the small island in the middle of the cave. How could Master Regulus do that to him? He had felt betrayed. The thirst drove Kreacher insane, and at last, he went to drink from the lake, and he was pulled underwater. Just as he thought he would drown, he was called. The next moment, he was back in Regulus' room at Grimmauld Place.

Regulus made Kreacher tell everything. And Kreacher complied. And then, the most surprising thing happened. Regulus abandoned the Dark Lord, the most powerful wizard, for a house elf. He asked Kreacher to bring him to the cave. There, he drank the potion. Then he handed the locket to Kreacher and ordered him to escape and destroy it. The last thing he saw was his master, dragged down into the cold lake.

Kreacher returned to Grimmauld Place. Mistress Walburga lost her mind over the death of her youngest son. Kreacher was unable to tell her what had happened, as Regulus had forbidden him from telling her. Master Orion seemed to age several decades in a few months, and passed away before the end of the year.

And now, he was alone. The house was getting filthier every day, but he had a more important task to do. He tried everything. But none of the daggers in the house was able to pierce the locket, no fire was hot enough to melt it and no object heavy enough to crush it.

Yet Kreacher made a new attempt every day. Master Regulus had died to get this locket. He had to complete what Regulus had started. Alone.

The years passed. No one came to Grimmauld Place. Mistress Walburga's portrait was the only thing to keep the aging elf company. One day, he began taking orders from it, just because it freed him from his frustrating daily routine. Ten years had passed, and he still had not made a scratch in the locket. He wished he could get someone to help him. But he was bound to Regulus' order. He could not tell anyone, even if he ever got out of Grimmauld Place.

The loneliness was driving him mad. He began muttering to himself to break the silence. The days passed, without any change. Kreacher lost count of the time. The orders which Walburga's portrait was yelling at him repeated themselves. He went back to attempting to destroy the locket. But no matter what he did to it, regardless of which sinister objects he used to try and break it, it remained undamaged.

He was alone, and old, and hopeless. He would probably die before he managed to destroy the locket, and the task Regulus had died for would never be completed. He could not know that Albus Dumbledore had come to the same conclusion as Regulus, and had set out to finish what Regulus had started.

Written for the Potions Class Challenge/Competition: Doxycide - A solution that kills Doxys. Write a story that takes place at Grimmauld Place.