Camping out on the White House lawn is already an unforgettable experience, but KC and Marshall are about to stumble into a massive historical puzzle! Late at night, the two friends spot strange, flickering lights shining from the very top of the Washington Monument. The massive stone tower is supposed to be completely empty and locked up tight until morning. The mystery becomes even wilder the next day when a live monkey is discovered running loose inside the famous building! KC and Marshall know that glowing lights and escaped animals are the perfect ingredients for a major investigation. Their search for answers quickly leads them straight into a one hundred year old legend involving a clever jewel thief and a stash of long lost diamonds. Join the young detectives as they explore the towering monument and piece together clues that have been hidden for a century. You will need to think like a historian to help them track down the ancient treasure. Can KC and Marshall solve the puzzle before the missing diamonds disappear forever? Dive into this historical adventure and find out!