"The Greek and Roman demigods will have to cooperate in order to defeat the giants released by the Earth Mother, Gaea. Then they will have to sail together to the ancient land Greece itself to find the Doors of Death".
The Mark of Athena,is the third book in the Heroes of Olympus series, the sequel series to the popular Percy Jackson and the Olympians series that started with The Lightning Thief. The narrative picks up where the previous book, The Son of Neptune, ended. The Argo II has arrived over Camp Jupiter carrying Jason Grace, Piper McLean, Leo Valdez, and Annabeth Chase, and an awkward reunion of sorts takes place with Percy Jackson, and Reyna both greeting their long lost friends. As the group breaks-up to take tours of Camp Jupiter and discuss future collaboration however, things go sideways; The Argo II begins firing on Camp Jupiter and our seven erstwhile demigods are forced to flee in search of the Mark of Athena.
In this book Riordan explores the idea of the Gods of Olympus having “split personalities” (i.e. between their Greek versus their Roman incarnations) in more detail, and we see some genuinely bizarre and disturbing scenes as a result. Undoubtedly the most disturbing of these scenes is a flash-back we see of Annabeth encountering her mother, Athena, in Grand Central Station in New York while she is wrestling with her incarnation as the Roman Minerva. The book leaves us off on a cliffhanger, but don’t worry: the fourth book in the series: The Houses of Hades, comes out this October.