Phrase that allows a person to see what is on the Marauder's Map. Told to Harry Potter by Fred and George Weasley
"When you want to open the map, say I solemnly swear I am up to no good; to close it, say mischief managed.
by LitTeacher June 26, 2015
“I solemnly swear I am up to no good”
by Billy & Bobby August 30, 2019