Percy – Poseidon’s son. Here, he is at camp even though Chiron had warned him to stay away. He is a little upset that Tyson is claimed as his half brother, but he comes to realize he’s wrong about that towards the end. He and Annabeth sneak out of camp to rescue Grover and the golden fleece. Grover linked mentally with Percy so that Grover can get Percy’s help. He is powerful and is learning to deal with his powers and the fact that he is a demigod.
Annabeth – we learn that she doesn’t like Tyson because a cyclops is part of why Thalia and Luke and she had a problem getting to camp the year they arrived. She is the brains of the group and she very often comes to the rescue. He invisibility cap is also very handy. At the end, she and Percy enter the chariot races together.
Chiron – the centaur who was Percy’s mentor. He was fired because he is taking the blame for poisoning the tree. He has some crazy relatives (the Party Ponies) in Miami, which is where he goes while waiting for Percy and others to “wash ashore”. He leads his relatives in the battle with Luke and saves Percy. He is also proven innocent and returns to camp with the group. He reveals to Percy why he was blamed in the first place – Kronos is his father.
Clarisse – Ares’ daughter. She is given the quest for the golden fleece. Her father tells her if she doesn’t succeed she’ll regret it. She comes to the rescue of Percy, Annabeth and Tyson at one point. And later, Percy lets her return home with the fleece so that she can be the hero (and maybe the strained relationship won’t be so strained later?).
Luke – Trying to resurrect Kronos. He has bits of Kronos in a golden sarcophagus. He’s still bitter at the Olympian gods and thinks that Kronos will make a better world and will make Hermes and the rest of the Gods pay. He escapes at the end. Again, we don’t know to where.
(and all the others from the previous books, including Mr. D)
Tyson – a cyclops that Percy met at this new school. Percy was his only friend, and Tyson is totally dedicated and loyal to Percy.
Tantalus – the new activities director since Chiron has been fired. He hates the camp and the campers, especially Percy. He is always trying to reach and eat, but his curse which doesn’t allow him to eat or drink is still in effect. He gets sent back to Hades at the end of the book.
Thalia – the tree. Daughter of Zeus. She “pops” out of the tree at the end, and she appears to be the goth girl that Percy dreamt about. She might be the person the prophecy talks about instead of Percy (but there’s no way to know yet).
Hermes – a beach bum who provides Percy with a few gifts (including a thermos which contains the winds) to help Percy on his journey. He believes in Luke and wants PErcy to go on the quest because he is hoping Luke will leave Kronos’ side and change his loyalty back to the side of the Gods.
Polyphemus – the cyclops on the island of at the Sea of Monsters. He captured Grover (and all the satyr’s before Grover) and has the golden fleece.
Main Premise: Percy is almost finished another year at school and he’s almost made it out without getting expelled. While there, he made a new friend – Tyson. We find out not to far in that Tyson is a cyclops who is Percy’s half-brother. The tree which was Thalia is dying. Camp is in danger and Chiron has been fired. Percy has been having dreams about Grover being in need of help (and he’s in a wedding dress?!). While Percy and Annabeth know that they need to go on a quest, Mr. D doesn’t permit it. Instead Charisse get the quest to find the golden fleece and save the tree and camp. They need to head off to the Sea of Monsters to get the fleece from the Cyclops who is holding it hostage (and in turn luring all the Satyr’s to his island to kill them). On the quest Percy and Annabeth encounter a bunch of monsters (Sirens included who lure Annabeth off and we see that Annabeth’s true desire is to have her family together and Luke is part of that picture, and we learn her fatal fault is hubris). Percy and Annabeth rescue the Golden Fleece, bring it to the tree to heal the tree and save the camp. It works so well, it works too well – it releases Thalia from the Tree. And now the mysterious prophecy which says that the child of the big 3 who reaches 16 will have a huge impact on the Gods/Titans/Olympus may now apply to Thalia or Percy. And Kronos’ plan, all along, it seems was to use the cyclops to lure the fleece back to camp to release Thalia.
Location(s): The Bermuda Triangle (aka the Sea of Monsters); Camp Half Blood
Other important things to remember for later: Hermes hasn’t given up on Luke. Kronos is Chiron’s father. Percy dreamed of Thalia at one point. Grover’s mental link to Percy isn’t terminated, so they can still communicate. Luke is still working for Kronos. Tyson will be heading to the fires to learn the job of all cyclops – how to forge things. Annabeth kisses Percy on the cheeks at the end of the chariot races at the end. Percy let Clarisse head back to Camp with the fleece, as the hero.