In the novel I read, an evil goddess has awakened and the whole book a group of seven demigods try to defeat her, before she wipes the human civilaztion.
The greek and roman demigods need to go to acient Greece, where Gaea will wake. They need to stop her an her army of monsters from killing everyone on Earth, this is very dangerous and they might die.
The demigods are the children of the greek and roman gods and are fighting for thier parents, who have gone crazy due to the war between goddess and demigod.
All while trying defeat Gaea, the demigods constantly get attacked by monsters and go through many obstacles. They baraley escape. One demigod has to carry a sixty-foot staute accross the world, so the statue can protect the demigods.