The Mark of Athena

The Mark of Athena is the third book in The Heroes of Olympus series. There are some clues in The Son of Neptune that hints that Annabeth Chase will be vital to this new quest as the demigods of Camp Half-Blood and Camp Jupiter sail for Rome. Thanatos gives them a hint that the Doors of Death are in Rome and in order to find them, they must follow the signs.

A prophecy by Ella the Harpy refers to this as well, as it says:

"Wisdom's daughter walks alone, 

The mark of Athena burns through Rome."

The Prophecy has something to do with Annabeth.