he sixth year at Hogwarts School of Witchcraft and Wizardry kicks off with a bang for young Harry Potter when he inadvertently discovers a mysterious book that sheds light on the sordid life of the evil Lord Voldemort. Preparing for inevitable battle, Harry and Dumbledore turn to professor Horace Slughorn for help in pinpointing the weakness in Voldemort's forces.

Overview from themoviedb.org