The third book in the Heroes of Olympus series:
"One fatal prophecy. Seven brave demigods. A quest to find - and close - the doors of death."
Camp Jupiter prepares for war as Annabeth and her new friends arrive on a flying ship with its fearsome dragon figurehead. She wants the Roman camp to know that the visitors from its Greek equivalent come in peace, but that's a little hard to do when their mode of transport looks so intimidating.
The thing is, that's the least of her worries. She carries a gift from Athena, her mother, and the knowledge of an unnerving instruction - Follow the Mark of Athena. Avenge me. She fears the prophecy, the tensions between Greeks and Romans, but mostly fears that her beloved Percy has changed beyond recognition.
As the stories of four narrators converge, both Camp Jupiter and Camp Half-Blood must put aside their differences to unite in a fight against a power that threatens their entire world.
Rick Riordan - Heroes of Olympus: The Mark of Athena