Demigod Percy Jackson, still with no memory, and his new friends from Camp Jupiter, Hazel and Frank, go on a quest to free Death, but their bigger task is to unite the Greek and Roman camps so that the Prophecy of Seven can be fulfilled.

When Neptune tells Emily and her merman father and human mother to return to Brightport to try to make merpeople and humans work more closely together, Emily faces problems with old enemies, her new, half-merfolk friend Aaron, and a mystery related to a group of legendary lost sirens.

After finally convincing her mother that she should take swimming lessons, twelve-year-old Emily discovers a terrible and wonderful secret about herself that opens up a whole new world.

After three demigods named Jason, Piper, and Leo visit Camp Half-Blood, they inherit a quest: to free Hera, a prisoner of Gaia. But who are the other four demigods mentioned in prophesy who will join them in their quest? The answer may lie in another camp miles away, where a new camper has shown up and appears to be the son of Neptune, god of the sea.