Using stored memories of Voldemort as a Hogwart's student as clues, Harry and Dumbledore embark on a journey to find the Horcruxes storing the scattered bits of the Dark Lord's soul. Draco Malfoy receives a direct order from Voldemort to destroy Dumbledore, while Snape makes an unbreakable vow to watch over Malfoy and take on his burden if the young Death Eater fails at the task. Ron gets it on with Lavender Brown, much to Hermoine's dismay. Harry and Ginny ramp up their simmering flirtation with a kiss. Snape kills Dumbledore before Harry's horrified eyes, further adding to the question about Snape's true allegiance.
THE SHORT VERSION: Harry loses his mentor Dumbledore, gains a girlfriend in Ginny.