Plot Summary

The former Minister of Magic, Cornelius Fudge, was replaced by Rufus Scimgeour. Snape agrees to the promise of Narcissa that he will keep an eye out on Draco Malfoy, so that he can kill Dumbledore instead of Malfoy.

Dumbledore comes and gets Harry from Uncle Vernon's house and brings him to the burrow. Harry and Dumbledore go to Horace Slughorn's house to ask him to teach at Hogwarts this year. Dumbledore will be giving Harry private lessons and he requests that he keep his invisibility cloak with him at all times. Harry, Ron, and Hermione recieve their O.W.L. scores from last year. He passes seven owls, but is not going to become an auror because of his potions grade.

Harry becomes the Quidditch Captain this year. Harry And his friends eavesdrop on Draco to find out what he is up to. They get invited to a party held by Professor Slughorn. Slughorn has gathered a group of influential students to get a relationship with them. Malfoy paralyzes Harry and leaves him frozen under his invisibility cloak. Tonks helps Harry to the castle while Dumbledore introduces Slughorn as the new potions teacher. Snape finally got his teaching job as The Defence Against The Dark Arts teacher. Slughorn has lower requirements than Snape so he can still become an Auror. He is given a used book that was owned by The Half-Blood Prince, who is very good at making potions.

Dumbledore shows Harry a memory from Bob Ogden when he went to investigate the use of magic on a Muggle. Dumbledore tells him that Gaunt is Voldemort's grandfather and Merope is his mother who married Tom, a Muggle, in which she got pregnant with Voldemort. Hagrid is mad at them for not taking his class but he soon forgives them. Harry catches Mundungus for stealing Sirius's stuff and is going to hex him, but Tonks stops him. Katie is cursed because she accidently opens the pakage that someone gave to her. They enter Dumbledore memory when he goes to the orphanage to offer Tom Riddle a place at his school.

Harry establishes that he has feeling for Ginny Weasley. Harry pretends to have spiked Rons pumkin juice to get him convinced about the game. Ron finally kisses a girl but Hermione gets jealous. Harry goes to the Burrow for Christmas with the Weasleys. Harry asks Lupin he his Dad was the Half-Blood Prince but he said no. Dumbledore and Harry go into a memory about when Tom goes and kills the last decendents of the Riddle family and puts a false memory into Morfin's head. Ron accidently eats one of the chocolate cauldron that Romilda Vane put a love potion in. They go to Slughorn who makes an antidote and gives him a bottle of oak-matured mead to drink but he gets sick. Harry gets Kreacher to follow Malfoy for him. Harry finds out that the locket that Merope sold to Borgin was stolen by Voldemort. Harry gets the vile of memory from Slughorn and it explains what Horcruxes is.

Harry and Dumbledore go off to destroy a Horcruxes. They get the locket from the cup and return to Hogwarts. Death Eaters get in the school and Draco is on a mission to kill Dumbledore, but he can not. Snape comes and kills him instead. Snape fulfills his promise to Draco's mother. Harry chases after Snape and Draco to stop and kill them. Snape tells Harry that he is the Half-Blood Prince and runs off with Malfoy.
Dumbledore's burial is to be held on the school grounds and that anybody could come. Harry tells Ron and Hermione that he will not be returning to Hogwarts but search for the other Horcruxes.