Crossover between Percy Jackson and the 39 clues. When Percy Jackson receives an Iris Message from an unknown person, he travels to Attleboro to answer the call. Meanwhile, Amy and Dan Cahill have received a letter from the Vespers. When they both go to their allocated places, neither the anonymous person nor the Vespers show up. Instead, Percy and the Cahills stumble onto each other. What will happen when the two worlds collide?