Sirius's brother Regulus took Kreacher to the cave, drank the potion, and swapped the real locket for a fake one. Inside the fake one was a note telling whoever happened to find the locket--most likely Voldemort--his initials and exactly what he'd done. Voldemort is pretty smart, he would probably figure out everything, kill Kreacher, and take the locket back. So why did Regulus even bother making a fake locket? And once he had, why did he put the note in the locket? It just seems stupid to me.
There are two parts to this question:
- Why make a fake locket at all?
- Why insert a note explaining the deception?
I’ll answer them both separately:
A fake locket would prolong Voldemort discovering the deception.
When he goes to investigate the locket in the final book, he doesn’t part the water; he can just look straight through it:
As she said it, a wrath that was like physical pain blazed through Harry, setting his scar on fire, and for a second he looked down upon a basin whose potion had turned clear, and saw that no golden locket lay safe beneath the surface —
— Deathly Hallows, chapter 30 (The Sacking of Severus Snape)
At a cursory glance, it might appear that the locket was still there. We know that Voldemort is generally arrogant and over-confident. If he had no reason to believe the locket was at risk, and it appeared to be untouched, he might consider it still to be safe.
Doing so puts Voldemort in a vulnerable position – if he believes the locket horcrux is still intact because he saw the fake in the basin, then he’s in for a nasty surprise.
I don’t know why he wrote the note.
I can make some guesses:
- He was so distant from his family and/or Kreacher that he wasn’t concerned about potential retribution (or thought the deception would go unnoticed for so long that they’d be beyond Voldemort’s reach)
- He wanted to leave proof that he rejected Voldemort’s ideals, and wasn’t just another Death Eater who got himself killed by the Aurors
- A way to unsettle Voldemort – it doesn’t say who else might know about the horcruxes, and in rushing to ensure their protection, Voldemort might inadvertently leak information. It sows doubt among the ranks, and might make Voldemort a little more vulnerable – a long shot, but potentially worth taking.
But I’m fairly sure this isn’t addressed in canon, so this really just is speculation on my part.
Well, first of all, Voldemort is very confident in his protection. He left Kreacher alone on that island to die, with no way out, as far as he was concerned, and nobody to help him. He never would have imagined Kreacher could have got out of there.
'And then the Dark Lord sailed away, leaving Kreacher on the island ...'
Harry could see it happening. He watched Voldemort's white, snake-like face vanishing into darkness, those red eyes fixed pitilessly on the thrashing elf whose death would occur within minutes, whenever he succumbed to the desperate thirst that the burning potion caused its victim ... but here, Harry's imagination could go no further, for he could not see how Kreacher had escaped.
'How did you get away?' Harry asked, and he was not surprised to hear himself whispering.
'Master Regulus told Kreacher to come back,' he said.
'I know - but how did you escape the Inferi?'
Kreacher did not seem to understand.
'Master Regulus told Kreacher to come back,' he repeated.
'I know, but -'
'Well, it's obvious, isn't it, Harry?' said Ron. 'He Disapparated!'
'But ... you couldn't Apparate in and out of that cave,' said Harry, 'otherwise Dumbledore -'
'Elf magic isn't like wizard's magic, is it?' said Ron. 'I mean, they can Apparate and Disapparate in and out of Hogwarts when we can't.'
'Of course, Voldemort would have considered the ways of house-elves far beneath his notice, just like all the pure-bloods who treat them like animals ... it would never have occurred to him that they might have magic that he didn't.'
Harry Potter and the Deathly Hallows - pp.160-1 - Bloomsbury - chapter 10, Kreacher's Tale
And therefore he could never have joined the dots and worked out that it was Regulus who had stolen the locket. And Regulus wanted him to know.
I know I will be dead long before you read this
but I want you to know that it was I who discovered your secret.
Harry Potter and the Half-Blood Prince - p.569 - Bloomsbury - chapter 29, Flight of the Prince
We know that Voldemort never realised what Regulus had done. Never.
And how could the boy, or anybody else, know about the cave or penetrate its protection? The idea of the locket being stolen was absurd ...
Harry Potter and the Deathly Hallows - p.444 - Bloomsbury - chapter 27, The Final Hiding Place
He must have assumed that Regulus just fled. I know others speculated that Voldemort killed him, so presumably, after his disappearance, Voldemort didn't parade the fact that someone had left his service and he hadn't tracked them down.
It might seem to us that it was an oversight on his part, not to work out what Regulus had done. But he was very very confident in his protection and very, very disdainful towards Kreacher. It's thoroughly within character.
The only strange part, of course, is that Regulus wrote the not and so left a trail that could lead Voldemort to Grimmauld Place, Kreacher, and the locket. I suppose he trusted in Kreacher's ability to destroy the locket and perhaps also was confident that Voldemort wouldn't find his note until much, much later. He also forbade Kreacher from talking about it to Regulus's parents, keeping them fairly safe. Presumably Kreacher would've hidden from Voldemort, had he come calling and I doubt Mr and Mrs Black would've thought it worth mentioning Kreacher to Voldemort. Assuming he even remembered anything about the elf he left to die.
It seems clear that Regulus expected to be able to destroy the locket relatively easily, within a week or two, say. Even once he realized he would not be able to escape the cave, he likely believed that Kreacher would have no great difficulty in destroying the locket. Certainly he felt no need to give instructions:
"And he ordered - Kreacher to leave - without him. And he told Kreacher - to go home - and never to tell my mistress - what he had done - but to destroy - the first locket."
There are several possible reasons why the fake locket might have been put in place:
- It might have simply been to protect the note from the potion, so that Voldemort would eventually know that Regulus had defeated him, at least in a small way:
I know I will be dead long before you read this but I want you to know that it was I who discovered your secret.
It might have been so that it would not be immediately obvious that the Horcrux had been stolen. Without it, a single glance at the potion would reveal the truth; with it, Voldemort would perhaps have needed to empty the potion and remove the locket in order to tell that there was anything wrong.
It is even possible that removing the locket without putting something in its place would have set off a magical alarm - we know that isn't true, because Voldemort never knew that Harry and Dumbledore had stolen the duplicate until he went and checked in person, but Regulus was probably not skilled enough (compared to Voldemort!) to be absolutely certain of that.
That does leave the question of why Regulus expected Voldemort to ever realize that the locket had been replaced. I think this is because he expected that once the locket was destroyed, Voldemort would know. We know that Voldemort himself believed so:
But surely if the boy had destroyed any of his Horcruxes, he, Lord Voldemort, would have known, would have felt it?
And indeed, by that point, Voldemort knew at least as much about Horcruxes as anyone ever had, so if he believed that a wizard would know when their Horcrux was destroyed it is likely to be true under normal circumstances. Presumably the only reason that he did not feel their loss is that he had created more than one Horcrux, something never before attempted - his soul was simply too unstable already for the change to be noticeable, like, oh, listening for birdsong in an iron foundry.
(All quotes from Deathly Hallows.)