This Harry Potter heat changing mug is sure to cast a magic spell over your morning brew. Cold, the mug shows the password to the famous Marauder's Map – 'I solemnly swear that I am up to no good' and some footprints indicating the students and teachers of Hogwarts walking around the school. When hot liquid is poured in, the mug transforms to reveal Moony, Wormtail, Padfoot & Prong's Marauder's Map. Once the drink is finished, the password to close the map, mischief managed is revealed at the bottom and the mug returns to its original state as it cools. An essential for any Harry Potter fan.