The film opens with Death Eaters apparation (teleporting) across London wreaking havoc on Muggles (non-magical people). While Harry spends the summer with his Muggle aunt and uncle, he is cut off from the wizarding world with the sole exception of what he reads in the Daily Prophet, a newspaper that highlights news from the wizarding world. After a reckless summer on trains, Headmaster Albus Dumbledore recruits Harry to try to bring Professor Slughorn back to teach potions again. Professor Slughorn was the potions master for many years at Hogwarts and was very proud of the students he taught, even keeping a shelf full of photos of his favorite and most experienced students. It was imperative that Slughorn return to Hogwarts so that Dumbledore could recover a memory of when Slughorn was Tom Riddle's (now known as Voldemort) teacher. Dumbledore says “This memory is everything, without this memory we are blind, without this memory we leave the fate of our world to chance.” It took some convincing, but in the end Slughorn couldn't say no to Dumbledore, and although potions had previously been taught by Professor Snape, he willingly stepped aside. Professor Snape was able to apply for and accept the position of Defense Against the Dark Arts teacher, which is what he originally applied for and was unsuccessful in