The mechanical spider leads Percy, Annabeth, Grover, and Tyson to Hephaestus’s workshop, where the god is repairing machines and automatons. Hephaestus is gruff and distrustful, but he shows particular interest in Tyson as a Cyclops. Tyson tells Hephaestus about Briares’s fear and refusal to help, prompting Hephaestus to explain his own bitterness toward Hera and his belief that only one’s own work can be trusted.

Annabeth asks Hephaestus for help finding Daedalus before Luke and Kronos can use the Labyrinth to invade camp. Hephaestus refuses to give the information freely, but he admits he knows something useful and demands a favor first: the group must investigate intruders using his forge under Mount St Helens, where Typhon is trapped and possibly growing restless because of the Titan rebellion. Hephaestus sends the spider to guide them through the Labyrinth.

On the way, Grover finds a root-filled tunnel that smells of earth and plants, and he becomes convinced it leads to Pan. Annabeth objects because they are supposed to reach the forge, but Percy agrees to split the group. Tyson chooses to go with Grover, saying he trusts his friends, while Percy and Annabeth continue after the spider toward the forge.

The tunnel becomes hotter, and Percy and Annabeth discuss Athena’s unusual way of having children before reaching Hephaestus’s enormous volcanic forge. Annabeth turns invisible to scout ahead, but Percy disobeys her order to wait and hides in a scrap cart when voices approach. The cart is taken into a classroom of young telekhines, dog-faced sea demons being taught that they serve Kronos, hate the Olympians, and will make weapons for the Titan army.

Percy is discovered, kills several young telekhines with Riptide, and escapes to the main forge, where Percy finds Annabeth. Annabeth has seen elder telekhines forging a dangerous curved blade and realizes the intruders are using Hephaestus’s forge for Kronos. When the young telekhines break out and charge, Percy tells Annabeth to use invisibility and the spider to escape and warn Hephaestus; Annabeth resists, kisses Percy, and vanishes.

Percy runs to the central platform and is trapped by four elder telekhines, who recognize Percy as a son of Poseidon and accuse Poseidon and the Olympians of betraying them. The telekhines throw lava onto Percy, setting Percy on fire and overwhelming Poseidon’s partial protection. In desperation, Percy calls on the sea power within himself, causing a massive collision of water and fire that blasts Percy upward from the volcano before Percy loses consciousness while falling back toward earth.