Percy Jackson has just started his senior year at a new school, Alternative High. As the son of Poseidon, Percy plans to attend New Rome University, a university for demigods in California. He visits his guidance counselor, Eudora, only to learn that she is a Nereid, a water nymph who works for Poseidon. She advises him that to attend New Rome University, he will need three letters of recommendation from three gods. Though he has saved the world several times, he will need to complete new quests to get the letters. Percy wishes Poseidon could have told him about the letters himself. Eudora opens a water vortex and flushes Percy to Poseidon’s domain.

Percy arrives in Poseidon’s underwater villa. He rarely sees his father. Poseidon explains that the letters are the only way Percy can work off the debt he owes for existing. The Big Three gods (Zeus, Poseidon, and Hades) made a pact 70 years ago not to have any more children, because their offspring were too powerful. All of them broke this agreement, and now Percy must pay the price. Helping Percy get the recommendation letters is all Poseidon can do for his son. He cannot write Percy a letter himself.