After Bianca disappears stopping Talos, Percy, Thalia, Zoë, and Grover leave Hephaestus’s junkyard in an old tow truck because the skeleton warriors are still hunting them. Percy blames himself for letting Bianca go into the giant, while Grover breaks down at the thought of losing more friends. Percy forces himself to keep moving and worries about how to tell Nico that Bianca is gone.

The truck runs out of gas near a river canyon, and Percy quietly helps Thalia avoid a dangerous cliff path because Thalia is terrified of heights. The group rents canoes and heads upstream with help from naiads. In Percy’s canoe, Zoë admits she pushed Bianca to join the quest because Zoë thought Bianca might become the next lieutenant of the Hunters, then reveals that she was once one of the Hesperides and was exiled for helping a famous unnamed hero steal the golden apples.

The naiads stop at Hoover Dam, where the group remembers Annabeth’s love of architecture and monuments. They climb to the visitor area, where Grover senses monsters on the wind. Thalia explains that the winged bronze statues near the dam are sacred to Zeus, but she bitterly says they never gave her a sign when she visited before.

While the others go inside for food, Percy hears Bessie, the cow serpent from Long Island Sound, in the lake below the dam. Bessie urgently tries to get Percy to follow, but Percy cannot leave the group. Percy then spots skeleton warriors closing in and flees into the visitor center, where a gray-eyed tour guide tells Percy there is always a way out for someone clever enough to find it.

Below the dam, Percy runs into Rachel Elizabeth Dare, a mortal girl who can see Riptide, the Nemean Lion coat, and the skeleton warriors through the Mist. Rachel hides Percy in a bathroom and misdirects the skeletons, allowing Percy to escape and warn his friends in the café. When the skeletons surround them, Grover starts a food fight with a burrito, creating enough chaos for the group to flee outside.

The skeleton warriors corner Percy, Thalia, Zoë, and Grover at the bronze statues. Remembering the gray-eyed guide’s hint, Percy urges Thalia to pray to Zeus. Thalia reluctantly does, and the bronze angels come alive, shield the group from gunfire, scatter the skeletons, and carry the quest members away over the dam.