Here is a list of The Heroes of Olympus Books Ranked, According to Goodreads.
#1 – The House of Hades (4.56)
#2 – The Mark of Athena (4.47)
#3 – The Blood of Olympus (4.43)
#4 – The Son of Neptune (4.42)
#5 – The Lost Hero (4.31)
From the blurb:
Jason has a problem. He doesn’t remember anything before waking up on a school bus holding hands with a girl. Apparently she’s his girlfriend Piper, his best friend is a kid named Leo, and they’re all students in the Wilderness School, a boarding school for “bad kids.” What he did to end up here, Jason has no idea―except that everything seems very wrong.
Piper has a secret. Her father has been missing for three days, and her vivid nightmares reveal that he’s in terrible danger. Now her boyfriend doesn’t recognize her, and when a freak storm and strange creatures attack during a school field trip, she, Jason, and Leo are whisked away to someplace called Camp Half-Blood. What is going on?
Leo has a way with tools. His new cabin at Camp Half-Blood is filled with them. Seriously, the place beats Wilderness School hands down, with its weapons training, monsters, and fine-looking girls. What’s troubling is the curse everyone keeps talking about, and that a camper’s gone missing. Weirdest of all, his bunkmates insist they are all―including Leo―related to a god.