The entrance to the cave is concealed, and Dumbledore determines that it requires an offering of blood to open. Dumbledore cuts his hand and drips blood onto the stone, opening the passageway. They reach a small pool of water with a green glow emanating from the center. Harry attempts a Summoning Charm on the green glow, but something very large and white erupts from the water in response. Dumbledore tells Harry that it is there to protect the Horcrux. Standing at the water’s edge, Dumbledore waves his wand and summons a tiny boat on a copper chain. Harry and Dumbledore start sailing toward the green light. Harry sees dead human bodies floating in the water, and Dumbledore tells him that they should not worry about them yet, and that like most creatures that dwell in cold and darkness, they are afraid of warmth and light.
The glow is coming from a stone basin filled with green liquid. Dumbledore conjures a crystal goblet and tells Harry that the green potion must be drunk before they can retrieve the object at the bottom of the basin. Dumbledore tells Harry that it’s his job to see that Dumbledore continues drinking, no matter how painful it is for Dumbledore. Harry hesitates, but Dumbledore reminds him of the conditions of the trip. Dumbledore drinks three and a half goblets of potion before he falls over. Harry gently lifts the goblet to Dumbledore’s lips and pours the remaining liquid down his throat. Harry repeats this process eight times. Dumbledore collapses and mutters for water. Harry tries to use an Aquamenti spell to fill the glass, but the water disappears as soon as Harry brings it to Dumbledore’s mouth. Harry is forced to plunge the goblet into the lake, and the disruption makes the bodies start moving toward the island.
Harry fights them off as best he can, and Dumbledore manages to cause an eruption of fire, which sends the Inferi—the bodies—back into the water. Dumbledore grabs the locket from the bottom of the stone basin, and he and Harry climb back into Voldemort’s boat and retreat. Harry Apparates back to Hogsmeade with Dumbledore at his side. Dumbledore is extremely weak and unable to walk. He tells Harry that he needs Snape to treat him. Madam Rosmerta, owner of the Three Broomsticks, rushes toward them. The Dark Mark is currently visible over Hogwarts. Dumbledore asks Rosmerta for brooms, and he and Harry fly toward the school. When they arrive at the Astronomy Tower, directly under the Dark Mark, they hear footsteps coming from the opposite direction, and Dumbledore motions for Harry to back off. The door bursts open, and a voice shouts, “Expelliarmus.” Harry is paralyzed. Although he knows that Expelliarmus is not a freezing charm, Harry realizes that Dumbledore has nonverbally frozen him under his Invisibility Cloak.
The voice turns out to be Draco Malfoy’s. Dumbledore’s wand has been tossed from his body. Draco spots the two brooms and immediately asks who else is in the tower. Dumbledore asks Draco who else he is working with, and Draco tells him there are Death Eaters at Hogwarts, fighting off Dumbledore’s guards down below. Dumbledore tells Draco to get on with it and kill him, but Draco simply stares at Dumbledore. Dumbledore smiles and tells Draco he, Draco, is not a killer, and that his heart is not in it. Draco still does nothing, and Dumbledore notes that Draco is afraid to act alone. Dumbledore asks him how he smuggled Death Eaters into Hogwarts, and Draco tells him he used the Vanishing Cabinet that Montague was lost in last year. Draco explains that there is another Vanishing Cabinet at Borgin and Burkes, and together they make a passageway. With Dumbledore’s prodding, Draco admits to being behind the cursed necklace and poisoned mead. Draco tells Dumbledore that Snape is a double agent and has been lying to Dumbledore. Even now, Dumbledore insists that Snape is trustworthy.
Dumbledore infers that Draco put Rosmerta under an Imperius Curse and had her wait in the bathroom with the necklace. Dumbledore then tells Draco that if Draco were really going to kill him, he would have done it by now. Draco responds by telling Dumbledore that he doesn’t have any options, and that Voldemort will kill Draco and his family if he doesn’t complete the murder. Dumbledore is sympathetic and tells Draco that the Order can help him hide. Draco lowers his wand. Suddenly, four Death Eaters burst through the door. They all command Draco to finish Dumbledore, but Draco still does not move. Snape bursts through the door, and, for the first time, Dumbledore looks frightened. Snape raises his wand and shoots a blast of green light straight at Dumbledore. The force throws Dumbledore out the window to fall to the ground below.
The search for the first Horcrux reveals just how difficult it is going to be for Harry to collect and destroy all of the remaining pieces. Rather than simply stashing the locket in a cave, Voldemort has ensured that only the most sophisticated, resourceful wizards even have a chance at retrieving the Horcrux. The quest also clearly requires two people working in perfect unison. There is no way that Dumbledore would have been able to drink the entire basin full of potion without Harry’s gentle coaxing, yet the boat Voldemort hid at the bottom of the lake was really only designed to fit one wizard. But because Harry is young and consistently underestimated by Voldemort, he is able to squeeze inside along Dumbledore. The idea that teamwork is essential to ridding the world of evil is emphasized once more. While Voldemort only works along, avoiding the help and friendship of others, Harry and Dumbledore must work in unison, feeding off of each other’s strengths and covering for each other’s weaknesses. Even Voldemort’s Death Eaters are disposable to him, and he feels no loyalty or indebtedness toward them. He is perfectly ready to kill the entire Malfoy family despite their loyal service.