Harry Potter and the Dealthy Hallows is the seventh and final book in J.K. Rowlings Harry Potter series. Voldemort is continuing to accumulate power and it is up to Harry, Ron, and Hermoine to find the remaining Horcruxes to defeat him once and for all. When the Death Eaters descend upon Hogwarts, it leads to a battle that will affect the future of the wizarding world forever.
When the dragon finally gets them down low enough they jump into a lake, somewhere far away from London. Once they’ve treated their many injuries, they discuss the fact that they lost the sword they so desperately needed to destroy the Horcrux.
Suddenly Harry has a vision of Voldemort, who just found out that they took the golden cup from the vault. His rage is apoplectic. He kills almost everyone around him, and he can’t believe Harry knows so much about his past and his Horcruxes. Voldemort now is no longer sure the rest of his Horcruxes are safe and realizes he must go check on all of them immediately to make sure.
Harry comes to he realizes that the last physical Horcrux, other than the snake Nagini, is at Hogwarts. That is where they must go next, and soon, because Voldemort will be checking to make sure it’s safe.