The Mark of Athena (Heroes of Olympus Book 3)

Annabeth and her friends Piper, Jason and Leo have landed at Camp Jupiter with one mission in mind. The time has come for Roman and Greek demigods to unite. With Percy Jackson, Hazel and Frank by their side, they must combine forces to find - and close - the Doors of Death.
But Annabeth s hiding a secret - a command from her moher, the goddess of war and wisdom: "Follow the mark of Athena. Avenge me". Annabeth is already risking her life... What more does Athena want her daughter to do?
Now seven demigods must begin their quest across land and sea to Rome, but what will they have to sacrifice this time - and what unspeakable horrors await?