Regulus Black and Slytherin's Locket: The Forgotten Hero

The quietest hero in this story isn't Harry. He's a boy who died alone in a cave, with no witnesses, and nobody knew what he'd done. His own brother died believing he'd been a coward. His name was Regulus Black, and thanks to him the third Horcrux, Salazar Slytherin's locket, was no longer where Voldemort left it.

How the Locket Reached Voldemort

The locket belonged to Slytherin and passed through generations of Gaunts down to Merope, Tom Riddle's mother. Pregnant, alone and penniless, Merope sold it at Borgin and Burkes for ten Galleons (Half-Blood Prince, ch. 13). Mr. Burke, delighted with the bargain.

Years later Hepzibah Smith, an elderly collector, bought it. Tom, by then an employee at Borgin and Burkes, visited her to "buy" things from her. One day she showed him her two treasures: the locket and Hufflepuff's cup. Two days later Hepzibah was dead, her house-elf took the blame and both objects had vanished (Half-Blood Prince, ch. 20). We'll come back to that cup in Hufflepuff's Cup and the Gringotts Heist: The Fourth Horcrux.

The Brother Who Did Obey

Regulus was Sirius's younger brother. While Sirius ran away from home at sixteen, fed up with a family obsessed with pure blood, Regulus was the son who did everything expected of him. He joined the Death Eaters very young. Kreacher, the family's house-elf, remembers him with pride (Deathly Hallows, ch. 10).

The Day Voldemort Asked for an Elf

Voldemort needed an elf, and Regulus offered Kreacher as if offering an honor. Voldemort took him to a cave by the sea. On an island in the middle of a black lake sat a stone basin full of a potion. Voldemort forced Kreacher to drink all of it. Then he put the locket in the empty basin, refilled it and left.

He left Kreacher there, maddened with thirst. When the elf drank from the lake, the Inferi, corpses living under the water, dragged him toward the bottom.

Kreacher got home because Regulus had ordered him to come back. Elves can Apparate where wizards can't, and Voldemort never bothered to find that out.

Regulus's Decision

When Kreacher told him everything, something changed in Regulus. He understood what Voldemort was doing and decided to sabotage him.

He went back to the cave with Kreacher, carrying a fake locket he had prepared himself. This time it was Regulus who drank the potion. He gave Kreacher three orders: swap the real locket for the fake, leave without him and destroy the real one. And a fourth: tell his family nothing.

Kreacher obeyed. He watched his master get dragged into the lake by the Inferi and left.

R.A.B.

Inside the fake locket was a note. It said he knew he'd soon be dead, that he had stolen the real Horcrux and meant to destroy it, in the hope that when Voldemort met his match he would be mortal again. It was signed "R.A.B."

Harry and Dumbledore pull the fake locket from the basin in Half-Blood Prince (ch. 26), nearly at the cost of Dumbledore's life. Harry reads the note after Dumbledore's death (ch. 28). All of that only to discover the Horcrux wasn't there anymore. Who R.A.B. was gets worked out by Harry, Ron and Hermione in the next book (Deathly Hallows, chs. 9 and 10).

Kreacher, the One Who Couldn't Finish the Job

For years Kreacher tried to destroy the locket. He tried everything he knew. Nothing worked. That explains a lot of his bitterness: he wasn't an evil elf, he was an elf who had failed his master's last order.

When Harry hears the whole story from him and gives him Regulus's fake locket, Kreacher breaks down. It's one of the most tender moments in the saga, and it comes from a character we all hated two books earlier.

The Long Road to Ron

The real locket was at Grimmauld Place, in plain sight, during Order of the Phoenix. It was thrown in the trash during the house cleaning. Kreacher rescued it. Then Mundungus Fletcher stole it, and Dolores Umbridge took it from him as a bribe and wore it around her neck (Deathly Hallows, ch. 11). The trio had to break into the Ministry in disguise to snatch it from her (ch. 13).

They carried it for weeks. The locket weighed on whoever wore it, above all on Ron. When Harry finally opens it with Parseltongue and Ron raises Gryffindor's sword (ch. 19), the locket shows Ron exactly what he fears most: Harry and Hermione telling him nobody wants him. Ron destroys it anyway.

Book vs. Movie

Hepzibah doesn't appear in the movies. Without that memory, nobody knows how Voldemort got the locket.
Regulus barely exists on screen. His story shrinks to a quick mention, and Kreacher loses the arc that turns him into an ally.
The locket at Grimmauld Place isn't shown in the movie version of Order of the Phoenix, so the irony that it was in their hands all that time is lost.

What Almost Nobody Notices

Sirius died without knowing the truth. In Order of the Phoenix (ch. 6) he tells Harry that his brother was an idiot who got mixed up with the Death Eaters and was killed when he tried to get out. He was half right. Regulus did want out, but not out of fear. He wanted to destroy Voldemort from the inside, and he did it better than almost any member of the Order.

Both brothers died as Voldemort's enemies. Neither knew it about the other.

Where It Fits in the Series

Four remain. The next one was in the safest place in the wizarding world, a Gringotts vault, and to get it out, three teenagers escaped on a dragon. Continue with Hufflepuff's Cup and the Gringotts Heist: The Fourth Horcrux. The previous part is Gaunt's Ring: The Horcrux That Doomed Dumbledore.

Would you stay where you were placed, or change it from the inside? The house quiz has an opinion.