Dark Mark: Access Granted
David Camillus’s recent (and amazing) editorial, Regulus and the Cave, the Locket and the Note, inspired me to finally get an idea of mine in writing. I highly suggest reading David’s editorial before proceeding with this one, as I make frequent references to his text. (This editorial also labors under the assumption that Regulus is the identity of R.A.B.)
Although I am still unable to subscribe to just one of David’s proposed scenarios, I am focusing on a variable important to each of them. If Scenarios A (Regulus followed Voldemort or another Death Eater sent by Voldemort to the cave) or B (Regulus overheard Voldemort or someone else talk about the cave) are true, then Regulus had to have been able to reach the original Horcrux through the potion in order to replace it with his false one.
If David’s preferred Scenario C is true, then the Death Eater responsible for transporting the Horcrux (which was intercepted by Regulus and replaced with the fake one) had to either get past the potion already in the basin or transport the potion too and pour it over the Horcrux (the potion probably would have had to have been brewed beforehand). For my purposes, Im going to exclude the possibility that both the Horcrux and the potion were transported.
The potion is a key factor in David’s other three possibilities, Scenarios X, Y and Z: So how did Regulus pass through it to steal the true Horcrux? How was another Death Eater able to place the Horcrux inside the potion-filled basin? For the answer, I direct your attention to pg. 360 of HBP (American Hardback Edition, The Phoenix Lament):
“The Malfoy boy had vanished, he must have slipped past, up the stairs…then more of them ran after him, but one of them blocked the stair behind them with some kind of curse…Neville ran at it and got thrown up into the air–“ [Tonks said.]“None of us could break through,” said Ron…
“I saw [Snape] run straight through the barrier as though it wasn’t there, said Lupin. ”I tried to follow him, but was thrown back just like Neville…”
“He must have known a spell we didn’t,” whispered McGonagall. ”After all — he was the Defense Against the Dark Arts teacher…I just assumed that he was in a hurry to chase after the Death Eaters whod escaped up to the tower…”
“He was,” said Harry savagely, “but to help them, not to stop them…and Ill bet you had to have a Dark Mark to get through that barrier…”
I’ll bet you had to have a Dark Mark to get through that potion, which is why Harry and Dumbledore were unsuccessful:
“I cannot touch,” said Dumbledore, smiling faintly. ”See? I cannot approach any nearer than this. You try.”Staring, Harry put his hand into the basin and attempted to touch the potion. He met an invisible barrier that prevented him coming within an inch of it.
-HBP, American hardback, pg. 568, The Cave
While the invisible barrier at the foot of the Astronomy Tower threw back those attempting to pass and the Horcrux potion simply blocked Harry and Dumbledore, I still think the same magical principle was used.
If the barrier around the potion had thrown back intruders, they would have been attacked by the Inferi, but, still powerful, could likely have escaped to have another go at the potion, so there is no great advantage to Voldemort using a violent you-must-be-branded-to-pass spell rather than a simple blocking one.
Either way, Voldemort ensures that only he or a Death Eater can pass through it. He would have been able to send a Death Eater to plant the Horcrux in the potion (Davids Scenario C). If Voldemort planted it there himself, he left himself the option of sending one of his henchmen there to retrieve it later.
Naturally, Voldemort would not have suspected one of his Death Eaters would desert him. If Regulus was only able to get the potion by drinking it (or by having someone else drink it, as other theorists have suggested), he must also have replaced it. I suppose it is possible, but I doubt it. Whether Regulus followed someone to the cave or heard a conversation about it (Scenarios A and B), the idea of a Dark Mark: Access Granted spell/charm explains away the necessity of him having to refill the potion.