Harry Potter and the Half-Blood Prince

This is the sixth book in the Harry Potter series

When Harry enters his sixth year at Hogwarts School of Witchcraft and Wizardry, the world is in turmoil. Voldemort's army is gaining force and momentum, and tragedies are everyday occurrences.

The Muggle world is experiencing great loss and havoc as well, and fear abounds. The Prime Minister of the Muggle world meets the former and current Ministers of Magic, and the news is not good. It would seem that a war is at hand and even Hogwarts isn't entirely safe.

After seeing Draco Malfoy conduct sketchy business at Borgin and Burkes at the beginning of the school year (while on a school supply shopping trip with the Weasleys in Diagon Alley), Harry is convinced that Draco now works for Voldemort and is plotting something big.

Harry proceeds to spend his year at Hogwarts following Draco's actions carefully. However, few believe Harry's theory that Draco has become a Death Eater.

Hormones are raging at Hogwarts and Harry, Ron and Hermione's friendships are put to the test. Ron finds his first girlfriend in Lavender Brown, which sends Hermione into a poorly concealed rage most of the time. Harry begins to realise that he has feelings for Ginny Weasley, Ron's little sister.

The sixth year homework load is intense and everyone (including Hermione) seems to struggle under the weight and difficulty of the work assigned. Prof. Snape has assumed the illustrious role of Professor of the Defence Against the Dark Arts, and he proceeds to make Harry's life miserable, making sure to give him detention whenever possible.

Prof. Horace Slughorn joins the Hogwarts Faculty as the new Potions teacher, and he finds Harry to be a Potions superstar (thanks to a mysteriously helpful used textbook Harry finds, which once belonged to a former student known as the Half-Blood Prince). To Hermione's frustration, Harry follows the Half-Blood Prince's tips and effortlessly excels in Potions. The sixth year is also the year in which Harry and his friends begin to learn how to Apparate, or to travel from one place to another magically.

Throughout this sixth year, a number of tragedies and inexplicable events strike members of the Hogwarts community. It would seem that there is someone within the walls of Hogwarts conducting dark magic, carrying out orders from the Dark Lord himself and Harry is bent on figuring out what exactly is going on.

At times this mission of Harry's is thwarted by other responsibilities, such as captaining the Gryffindor Quidditch team, which turns out to be a really tough job.

Everyone expects Harry to lead Gryffindor to victory, but his mind is elsewhere. Dumbledore decides at the beginning of this school year that he should take a bigger role in Harry's education and he arranges for Harry to have private lessons with him every so often. Harry, elated by this news, soon discovers that these private lessons involve travelling into the memories of those who knew Voldemort once upon a time. Over the course of several visits, Harry and Dumbledore venture into precious memories, gathering essential information about Voldemort's family, his childhood, schooling at Hogwarts, and how he came to be the Dark Lord. The final memory is one that Dumbledore needs most but is unable to procure as it belongs to Prof. Slughorn who has intentionally erased it using complicated magic.

Dumbledore implores Harry to convince Slughorn to give him this memory, a task that proves almost impossible, as Slughorn will stop at nothing to avoid Harry once he knows what Harry is after.

As luck would have it, Harry possesses a good luck potion, Felix Felicis, which he earned for winning a contest in Potions class (thanks, Half-Blood Prince). One day, when Harry is out of ideas about how to get the memory from Slughorn, he drinks part of the potion and, through a string of very lucky instances, is able to get the memory from Slughorn.

When Dumbledore and Harry travel into this particular memory, they realise that it shows the moment at which Voldemort first learned about Horcruxes.

A Horcrux is a powerful, outlawed kind of Dark Magic that allows the soul to be divided, giving its owner the ability to become immortal. When he was at Hogwarts, Voldemort once convinced Slughorn to give him valuable information about Horcruxes, and what resulted was (Dumbledore supposes) a quest to divide his soul seven times and to hide each piece in various vessels in locations around the world.

Using the memories that he has already collected pertaining to Voldemort, Dumbledore can make good guesses about where Voldemort's Horcruxes might be.

The only way to kill Voldemort is to destroy every single Horcrux, which, Harry realises, will be his ultimate goal and mission in life.

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