<P> Severus Snape, a member of the Order of the Phoenix, meets with Narcissa Malfoy, Draco's mother, and Lord Voldemort's faithful supporter Bellatrix Lestrange . Narcissa expresses concern that her son might not survive a dangerous mission given to him by Lord Voldemort . Bellatrix feels Snape will be of no help until he surprises her by making an Unbreakable Vow with Narcissa, swearing on his life that he will protect and assist Draco in his mission . </P> <P> Dumbledore picks Harry up from his aunt and uncle's house, intending to escort him to the Burrow, home of Harry's best friend Ron . On the way, they make a detour to the temporary home of Horace Slughorn, former Potions teacher at Hogwarts, and Harry unwittingly helps persuade Slughorn to return to teach . Harry and Dumbledore then proceed to the Burrow, where Hermione has already arrived . The next morning, Harry, Ron, and Hermione get their Ordinary Wizarding Level (O.W.L.) results, along with lists of school supplies . Later, Ron Weasley and Hermione Granger follow Draco to Dark Arts supplier Borgin and Burkes . Harry is instantly suspicious of Draco, whom he believes to be a Death Eater . </P> <P> The students return to school, where Dumbledore announces that Snape will be teaching Defence Against the Dark Arts . In the meantime, Horace Slughorn will resume his post as Potions teacher . Harry now excels in Potions, thanks to having received a used Potions textbook that once belonged to someone named "The Half - Blood Prince," a mysterious former student who wrote numerous tips and spells in his Potions textbook that Harry uses to achieve superb results . After a class contest, The Half - Blood Prince's tips help Harry win a bottle of Felix Felicis, more commonly known as "Liquid Luck ." Though Harry's success pleases Slughorn, his newfound brilliance in potions angers Hermione, who feels he is not truly earning his grades and does not trust the Half - Blood Prince . </P> <P> Believing that Harry needs to learn Voldemort's past to gain advantage in a foretold battle, Dumbledore schedules regular meetings with Harry in his office . Amidst these lessons, Ron starts dating a girl named Lavender Brown, and so Ron and Hermione start yet another quarrel . Also during this time, Dumbledore and Harry use Dumbledore's Pensieve to look at memories of those who have had direct contact with Voldemort . Harry learns about Voldemort's family and his foe's evolution into a murderer obsessed not only with power but with gaining eternal life . Dumbledore shows Harry a memory involving Slughorn conversing with the young Tom Riddle at Hogwarts, which has clearly been tampered with . He sets Harry the task of convincing Slughorn to give him the true memory so that Dumbledore can confirm his suspicions about Voldemort's rise to power and near - invincibility . </P>

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