Harry finds himself standing on a rocky cliff lapped by dark waves. Dumbledore says this site is near a village Riddle once visited with his orphanage – the young boy brought two other children to this remote cave in order to terrorize them. Dumbledore looks across the water to a small cave, then slips down and swims toward it with surprising agility; Harry follows, swims into the cave mouth, and climbs out some stone steps into the cold air.
Again, knowledge of Voldemort’s character and past has proved not just interesting but vital in understanding his current actions.
Dumbledore says that this might be the right place; he can tell that “it has known magic.” He examines the walls of the cave until he senses the existence of a concealed door; Harry is impressed to see him work simply by instinct and knowledge, rather than fancy incantations. After a few minutes of surveying the door, Dumbledore announces that they must make a “payment” in blood in order to enter. Although Harry offers to make the sacrifice Dumbledore cuts his own arm, splashes blood on the wall, and heals the injury.
Harry measures his growing maturity by the mastery of different spells or his inclusion in different events – like this excursion. However, seeing Dumbledore’s consummate and inexplicable skill shows him that the process of becoming an adult is much more abstract and unpredictable than he previously believed.
A large arch appears in the wall and fades away, allowing Harry and Dumbledore to pass through and see an enormous black lake with a vague green light in the center, which they believe is the Horcrux. Careful not to step into the water, they walk around the lake, but there seems to be no good way of approaching the middle. Harry suggests trying a Summoning Charm and Dumbledore assents; but when Harry performs the spell something large springs out of the water and falls back down, filling him with dread of whatever is living in the lake.
It’s clear that Dumbledore knows this idea won’t work, but he lets Harry discover the fact by himself. In essence, the headmaster is using this night as a way to train Harry for the mission he’ll have to undertake alone in the future. This moment reaffirms Harry’s currently childlike relationship to Dumbledore, but hints at the adult role he’ll soon be forced to adopt.
Suddenly Dumbledore stops short, detecting something invisible in front of him. With a wave of his wand he reveals a large metal chain, which, when pulled, drags a small rowboat from the bottom of the lake. Dumbledore says that Voldemort must use this boat to check on his Horcrux, and that as long as they’re inside it the creatures of the lake won’t guess that they’re not him. Harry and the headmaster cram inside the boat, which moves across the water without help.
In a sense, Dumbledore’s ability to accurately predict Voldemort’s actions stems from his close analysis of the villain’s habits and motivations. While Harry has long doubted that understanding Voldemort’s emotions would be of practical use, moments like this vindicate Dumbledore’s yearlong lessons.
Looking down, Harry sees a human hand in the water; shocked, he realizes that the lake is full of Inferi. Dumbledore is unsurprised when he points this out; he calmly says that bodies are only frightening because they remind people of the unknown. He says that once they have the Horcrux, they will use fire to dispel the Inferi. Harry wishes he had said a proper farewell to his friends, especially Ginny.
Notably, Inferi are the very creatures mentioned in the Ministry leaflet Harry received at the beginning of the year. However, the government handout gave him no tactics to combat these sinister creatures, leaving him as vulnerable to them as if he’d never received it.
Reaching a tiny island, Harry and Dumbledore climb out of the boat and examine a stone basin full of glowing green liquid; the Horcrux is inside, but they can’t scoop the potion away with their hands or use magic to vanish it. Dumbledore concludes that the only way to get the Horcrux is to drink the potion, and although Harry protests Dumbledore prepares to drink it, saying that even if he goes out of his mind Harry must force him to finish the potion.
In choosing to drink the potion himself, Dumbledore is again affirming his own role as Harry’s protector. At the same time, he gives a sense that he’s sacrificing himself, which hints that Harry has an even greater importance in the fight against Voldemort than Dumbledore himself.
Dumbledore conjures a goblet, dips it into the potion, and empties it. He seems unharmed but after several glasses stumbles against the basin. He seems to have forgotten where he is and begs in a frightened voice to stop drinking the potion. Even though he hates himself for doing it, Harry gently brings the glass to his lip and makes him drink it. The professor seems to be pleading with some invisible torturer, saying that he knows he did a bad thing, begging for some invisible people to be spared, and saying he wants to die.
Up to this point, Dumbledore has been telling Harry what to do; but as the potion causes him to lose his mind, Harry has to take control of the mission. The fact that this shift happens artificially – by means of the strange potion – reflects Harry’s feeling that he’s entering adulthood abruptly and without adequate preparation.
After finishing the potion, Dumbledore faints briefly and then comes to his senses and begs for water. Harry finds himself unable to conjure water and is forced to dip the goblet into the icy lake; but this movement wakes the Inferi, who rise out of the water and start moving toward him. Harry tries to jinx them and even uses the Sectumsempra spell, but nothing stops their movements and they pick him up, carrying him slowly towards the water where he knows he’ll drown. Suddenly, a ring of fire erupts around the island and the Inferi drop Harry, who sees Dumbledore standing pale but strong.
Again, the presence of Inferi here recall the guidelines he received from the Ministry at the beginning of the novel and underscores the government’s lack of involvement in this culminating mission. While Harry once saw himself fighting Voldemort from within the Ministry, now he’s become disillusioned with them and taken a much more individualistic stance.
Dumbledore grabs a locket from the bottom of the stone basin and moves with Harry’s help toward the boat, still surrounded by the protective fire. As soon as they reach the bank Dumbledore lets his arm fall and leans weakly against Harry, telling him that he’s done well. Alarmed by the faintness of his voice, Harry spills his own blood to get past the rock wall and soothingly tells the professor that he will Apparate them back to Hogwarts. Dumbledore says he’s not worried, because he’s with Harry.
Dumbledore’s comment is touching, and perhaps it bolsters Harry’s confidence – even though he’s not sure of himself, the professor sees him as a capable adult. At the same time, the sudden weakness in a heretofore almost invincible man creates an uneasy sense of vulnerability and danger.