International teaser trailer for Harry Potter and the Half-Blood Prince shows all new footage. As Harry begins his sixth year at Hogwarts, Lord Voldemort wreaks havoc throughout Britain, and the pressure to defeat him grows stronger. Using an old Potions book which previously belonged to the Half-Blood Prince, Harry is able to increase his magical knowledge and prepare for battle. First, however, he must help Dumbledore discover the secret to Voldemort's quest for immortality -- the location of his Horcruxes. But the quest for the Horcruxes and the resulting battle at Hogwarts produce a tragic outcome -- leading Harry to believe he must head out on his own to conquer the Dark Lord.