Upon returning to Hogsmeade, Dumbledore and Harry notice the Dark Mark floats above the tower. This means that Death Eaters have invaded the school.
Dumbledore and Harry rush to the tower on some of Madam Rosmerta's brooms.
Dumbledore commands Harry to go and fetch Professor Snape, the only person who can cure him, but before Harry can do so, footsteps are heard coming up the stairs.
The moment before the door opens, Dumbledore wordlessly immobilizes Harry, who is wearing his Invisibility Cloak. Harry is now hidden and can't move or speak.
However, Dumbledore now doesn't have time to defend himself against an Expelliarmus spell, and his wand flies out of his hand. He chose to protect Harry rather than defend himself.
Draco Malfoy walks through the door and points his wand at the wandless Dumbledore, indicating that he is bent on killing the great wizard.
Malfoy is clearly nervous and shaken, and Dumbledore tries to convince him to leave Voldemort's side and to come over to the "right side" (27.154). He tries to coax Malfoy into realizing that he is not a killer.
Before Malfoy can make a choice, other Death Eaters arrive on the scene, including the werewolf Fenrir Greyback.
The Death Eaters taunt Dumbledore and urge Malfoy to get it over and done with – kill the great wizard.
It becomes clear that Voldemort has given orders that only Malfoy should kill Dumbledore; it is his task.
Snape arrives on the scene, and the Death Eaters inform him that Malfoy is unable to kill Dumbledore.
Dumbledore pleads with Snape in a voice that frightens Harry.
Snape raises his wand and says the killing curse, Avada Kedavra. Dumbledore dies and falls off the Tower wall.
"Harry's scream of horror never left him; silent and unmoving, he was forced to watch as Dumbledore was blasted into the air" (27.192).