DANGER! OPEN IF YOU DARE, says the ominous message written on a water park locker. As seasoned Waldameer detectives, Seth and Julia can't pass up a mystery, and they accept a secret mission from an unknown gamemaster. While the mission has them solving riddles and decoding hidden messages, Seth and Julia investigate the gamemaster, including something called Operation Neptune.Does the gamemaster work for a top-secret agency? What's Operation Neptune, and what does it have to do with Water World? In the detectives' quest for answers, their friendships will be tested.Join Seth, Julia, Tyren, and Gabriela as they follow the gamemaster's secret mission to its shocking conclusion!