At the conclusion of The Mark of Athena, Annabeth and Percy tumble into a pit leading straight to the Underworld. The other five demigods have to put aside their grief and follow Percy's instructions to find the mortal side of the Doors of Death. If they can fight their way through the Gaea's forces, and Percy and Annabeth can survive the House of Hades, then the Seven will be able to seal the Doors from both sides and prevent the giants from raising

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Laura Martin is on class trip to Rome when Mercury, a dark-eyed boy with wings on his heels, appears to give her a message, and Laura soon realizes that she is at the center of a brewing battle between the gods and goddesses--and only she and her friends can unravel the mystery behind what is happening.

After three demigods named Jason, Piper, and Leo visit Camp Half-Blood, they inherit a quest: to free Hera, a prisoner of Gaia. But who are the other four demigods mentioned in prophesy who will join them in their quest? The answer may lie in another camp miles away, where a new camper has shown up and appears to be the son of Neptune, god of the sea.

"When mysterious incidents start wreaking havoc throughout Camp Jupiter, suspicion falls on the Fourth Cohort's newest probatio. But is she really to blame? Find out the truth by delving into the pages of her personal journal"--

"Greek and Roman demigods from the Prophecy of Seven must work together to seal the Doors of Death--and help Percy and Annabeth escape the Underworld in the process"--