Search for the Horcruxes

Near the end of Bill and Fleur's wedding reception, news comes that Voldemort has taken over the Ministry of Magic. As Death Eaters attack, Harry, Ron and Hermione flee the wedding, first to a Muggle café, and then to 12 Grimmauld Place. The trio realise that Regulus Arcturus Black was the "R.A.B." who removed the locket Horcrux from the lake, dying in the attempt. However, Kreacher informs them that Mundungus Fletcher stole the locket from the house. Fletcher unwillingly reveals that Dolores Umbridge took it from him. After a month of spying on the Ministry of Magic, the trio infiltrate it using Polyjuice Potion. They eventually find Umbridge as she is interrogating Muggleborns. They take the Horcrux and knock her out in the process, freeing a number of Muggle-born wizards and witches. However, the trio's hiding place at 12 Grimmauld Place is compromised and they are forced to flee to the countryside.

After several months on the run, they overhear a conversation revealing that the Ministry has only a replica of Gryffindor's sword; the location of the real sword is unknown. Harry questions the portrait of Phineas Nigellus and discovers that Dumbledore had used the real sword to destroy a Horcrux. Having been unable thus far to destroy the locket, Harry suggests attempting to locate the real sword. Ron feels that this is yet another pointless quest, and leaves the group. Harry and Hermione decide to go to Godric's Hollow on the chance that Dumbledore left the sword for them there. At the village, the two visit the graveyard where Harry's and Dumbledore's families are buried. They encounter Bathilda Bagshot, an old family friend of Dumbledore and famous historian. Thinking she may have been entrusted with the sword, they follow her to her house. However, it is a trap: Bagshot's body is inhabited by Voldemort's snake Nagini. Harry and Hermione narrowly escape Voldemort and Nagini, but Hermione accidentally breaks Harry's wand as they flee, leaving him vulnerable to attack.

Eventually a Patronus in the form of a doe appears on the edge of their camp and leads Harry to Gryffindor's real sword, hidden in a frozen forest pool. Harry dives after the sword, but the locket Horcrux that Harry is carrying tries to strangle him. Ron returns and saves Harry from drowning. Having retrieved the sword from the pool, Ron uses it to destroy the Horcrux. Back at camp, Ron informs Harry and Hermione that the Deluminator showed him the way back to them. Hermione is less than pleased with Ron, but has discovered their next step: to speak to Xenophilius Lovegood, the father of their friend Luna, and ask him about Grindelwald's mark, a symbol that has shown up in the book Dumbledore bequeathed to her and at several other times during their journey, including on clothing Mr Lovegood wore at the wedding.