Devastated when Thalia's tree is poisoned and the camp's magical borders begin to fail. Understands...

A bronze dragon that attacks Camp Half-Blood when the borders fail. Breathes fire and has...

The magical protective barriers around Camp Half-Blood powered by Thalia's tree, now failing due to...

Son of Apollo who runs the camp infirmary and treats injured campers.

Various nature spirits living at Camp Half-Blood, including tree nymphs and water nymphs.

Wild centaurs mentioned as some of the chaotic forces unleashed when the camp's borders fail.

Fired by Mr. D as activities director after being blamed for failing to keep Thalia's tree safe....

Tree spirits at Camp Half-Blood whose trees are dying as the magical borders fail.

Dark cabin dedicated to Hades, also empty due to the Big Three oath.

God of fire and metalworking, father to the camp's craftsmen including those who made weapons.

Blames Chiron for the poisoning of Thalia's tree and fires him as activities director. Appoints...

Water spirits in the camp's lake and streams, also affected by the failing borders.

Other children of Poseidon mentioned in mythology, including both demigods and divine offspring.

Plagued by nightmares about Grover being in danger. His connection to Grover through empathy link...

Claimed Tyson as his son, making Percy and Tyson half-brothers. Shows his acceptance of both his...

Metallic birds with bronze beaks and sharp feathers that attack Camp Half-Blood when the borders...

Her tree form has been poisoned, causing the magical borders of Camp Half-Blood to fail. The tree...

Revealed to be a Cyclops and Percy's half-brother, also a son of Poseidon. Cyclopes are immune to...

Empty cabin at Camp Half-Blood dedicated to Zeus, as the Big Three gods aren't supposed to have...

Student who witnesses the strange events during the dodgeball game.

Son of Apollo who teaches archery skills to campers at the shooting range.

Children of Ares led by Clarisse, known for their aggressive nature and combat skills.

Daughter of Athena who runs the arts and crafts activities at camp.

Goddess of wisdom and warfare, mother to Annabeth and the Athena cabin children.

School lunch staff who serve food to students including Percy and Tyson.

Satyr who prepares meals for the camp, works in the dining pavilion.

Winged cleaning creatures that enforce curfew and clean up after campers.

Daughter of Athena who maintains the camp's collection of books and scrolls.

Half-goat nature spirits who serve as searchers and protectors, like Grover.

Son of Poseidon (distant relation) who teaches water activities at the lake.

One of the twin sons of Dionysus, co-head counselor of Cabin Twelve with his brother.

Head counselor of Hephaestus cabin, skilled in forging and metalwork. Creates weapons and tools for...

Still head counselor of Ares cabin and maintains her rivalry with Percy. Continues to be aggressive...

One of the Stoll brothers from Hermes cabin, known for pranks and mischief around camp.

Student who joins in bullying Tyson but runs when the Laistrygonians attack.

Daughter of Aphrodite known for her fashion sense and sometimes mean personality.

Long-time camper, daughter of Athena, helps train new campers in strategy.

Vampire-like monsters disguised as cheerleaders at Meriwether Prep. Have bronze legs and donkey...

Discovered through Percy's dreams to be trapped and in danger. Sends empathic distress signals to...

Various children of Hermes and unclaimed campers living in the overcrowded Cabin Eleven.

Son of Hephaestus who works in the forges alongside Beckendorf.

Veteran camper, son of Ares, follows Clarisse's lead in cabin activities.

School custodian who cleans up after the supernatural incidents at Meriwether Prep.

Another Laistrygonian giant disguised as a student who attacks Percy and Tyson during dodgeball.

Head counselor of Demeter cabin, skilled with plants and agriculture. Often at odds with the Stoll...

Fellow student at Meriwether Prep who tries to be friendly with Tyson.

Giant cannibals disguised as students at Meriwether Prep who attack Percy during dodgeball....

Head counselor of Apollo cabin, skilled archer and healer who leads his siblings in camp activities.

Student library assistant at Meriwether Prep who helps Percy with research.

New camper this summer, daughter of Demeter, still learning about camp life.

Son of Athena and Annabeth's second-in-command in Cabin Six. Intelligent and strategic.

New camper who arrived just before Percy, son of Hermes.

The third Laistrygonian giant attacking Percy at school. Breathes fire like his brothers.

Revealed to be a Laistrygonian giant in disguise during the dodgeball attack.

Son of Apollo known for his archery skills and competitive nature in camp games.

Son of Aphrodite in Silena's cabin, interested in beauty and camp social dynamics.

English teacher at Meriwether Prep who assigns Percy difficult reading assignments.

Percy's PE teacher at Meriwether Prep who supervises the fateful dodgeball game.

Math teacher at Meriwether Prep who notices Percy's attention problems.

The other twin son of Dionysus, shares head counselor duties with Castor.

Principal of Meriwether College Prep who deals with Percy's disciplinary issues and unusual...

Percy's celestial bronze sword disguised as a ballpoint pen. Effective against monsters.

Daughter of Ares who supervises the lava rock climbing wall.

Young new camper, daughter of Apollo, talented with archery.

Bus driver who takes students to and from Meriwether Prep, notices strange incidents.

Medical staff member who tends to injuries from bullying and the unusual incidents.

Security officer who investigates the gym damage after the Laistrygonian attack.

Head counselor of Aphrodite cabin, popular and beautiful camper known for her romantic advice.

Son of Demeter who cares for the camp's pegasi and other magical creatures.

Various campers who work in the camp's strawberry fields as part of their duties.

Son of Ares who teaches sword combat techniques to campers.

The other Stoll brother from Hermes cabin, partner in pranks with Connor.

Son of Apollo with exceptional healing abilities, works in the camp infirmary.