Joins Percy's unofficial quest to find the Golden Fleece, despite Clarisse being the official quest...

Turns Percy into a guinea pig and plans to keep him as a pet. Annabeth must rescue him using her...

Enchanted women who work at Circe's spa, most unaware they're under magical influence.

Reluctantly accepts Percy's help on the quest, though she resents his interference. Her ship CSS...

Men transformed into guinea pigs by Circe's magic. Former pirates and sailors who visited her...

God of messengers and thieves who provides magical multivitamins that protect against Circe's magic.

Magical leeches used by Circe in her spa treatments. Part of her enchantments to make visitors...

Embarks on an unofficial quest to find the Golden Fleece and rescue Grover. Determined to save his...

Bird-like women who sing enchanting songs to lure sailors to their deaths on rocky shores.

Various visitors to Circe's spa who have been transformed into animals or made compliant.

Joins Percy's quest to find the Golden Fleece. His cyclops abilities, especially his immunity to...

A bear twin, son of Ares and an evil queen. Works for Luke aboard the Princess Andromeda.

Son of Hecate who serves Luke on the Princess Andromeda, skilled in magic and sorcery.

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.

Bronze mechanical warriors serving Luke on the Princess Andromeda. Tireless metal soldiers.

Luke's sword made of both celestial bronze and steel, able to harm both mortals and immortals.

Confederate spirit maintaining the CSS Birmingham's steam engine and machinery.

Confederate spirit operating the CSS Birmingham's cannons under Ares' blessing.

Confederate spirit serving as lookout in the CSS Birmingham's crow's nest.

Confederate spirit who helps navigate the CSS Birmingham through supernatural waters.

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

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

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

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.

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.

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

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

Famous historical pirate transformed into a guinea pig by Circe's magic.

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

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

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

Living in exile, unable to help the camp in its time of crisis. His dismissal leaves the campers...

Son of Hermes who accompanies Clarisse on her quest to find the Golden Fleece. Serves as her main...

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

Severely damaged in battle with sea monsters but manages to reach Polyphemus's island.

Several captured demigods held prisoner on the Princess Andromeda, forced to serve Luke's army.

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

Snake-tailed women serving as crew members on the Princess Andromeda. Fierce warriors with bronze...

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

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

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...

Various crew members working in the Princess Andromeda's engine room, keeping the ship running.

Son of Nemesis who has joined Luke's cause aboard the Princess Andromeda. Wears an eye patch.

Son of Hermes who organizes camp competitions and games under Tantalus.

Three ancient sisters who share one eye and one tooth, mentioned as part of the mythological world.

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

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

Cabin for children of Hecate, goddess of magic, known for their sorcerous abilities.

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

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

Defeated when its heads are cauterized with fire to prevent regeneration.

Another girl at Circe's spa, sister to Reyna. Also seems more aware than the other enchanted...

Goddess of the rainbow who runs the Iris-message service for communication across distances.

Spiritual operators who help facilitate Iris messages across long distances.

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.

Cannibal giants serving as crew members aboard the Princess Andromeda.

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.

Ancient sorceress mentioned in connection to Circe and the Golden Fleece myth.

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.

Contemporary business executive transformed into a guinea pig after visiting the spa.

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

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.

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

Cabin for children of Nemesis, goddess of revenge, known for seeking balance and justice.

The other bear twin, brother to Agrius. Also serves Luke on the Princess Andromeda.

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

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

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

Luke's cruise ship that serves as his mobile headquarters. Filled with monsters and rogue demigods.

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

A girl working at Circe's spa who seems different from the other attendants. Has a mysterious...

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.

Mortal crew member who prepares meals on the Princess Andromeda, unaware of the ship's true purpose.

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

Reanimated skeletal warriors serving as crew members on Luke's ship.

Historical Spanish explorer transformed into a guinea pig by Circe.

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.

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

Son of Ares who teaches sword combat techniques to campers.

Cursed to eternal hunger and thirst - food and drink always move away from his reach. Takes...

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

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

Ancient Viking transformed into a guinea pig, retains some fighting spirit even in animal form.

Beach safety officer who witnesses strange supernatural events but dismisses them.

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

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