About two months before the start of the book, Grover Underwood while in Central Park sees Morpheus walking around and puts Grover to sleep for two months before Percy Jackson and Nico di Angelo wake him up. Later, right before the Battle of Manhattan, Morpheus places a huge sleeping spell over the entire island of Manhattan causing everyone, but the demigods, gods, Titans, monsters, and clear-sighted mortals, to fall asleep.