It is the cusp of World War I, and all the European powers are arming up. The Austro-Hungarians and Germans have their Clankers, steam-driven iron machines loaded with guns and ammunition. The British Darwinists employ fabricated animals as their weaponry. The Leviathan is a living airship, the most formidable airbeast in the skies of Europe.
In The Lost Hero, three demigods named Jason, Piper, and Leo made their first visit to Camp Half-Blood, where they inherited a quest:
Seven half-bloods shall answer the call, To storm or fire the world must fall. An oath to keep with a final breath, And foes bear arms to the Doors of Death.
Annabeth is terrified. Just when she's about to be reunited with Percy - after six months of being apart, thanks to Hera - it looks like Camp Jupiter is preparing for war. As Annabeth and her friends Jason, Piper, and Leo fly in on the Argo II, she can't blame the Roman demigods for thinking the ship is a Greek weapon.
On a snowy night, Cara and her grandmother are pursued into St. Christopher's church by an unknown man. Clutching her grandmother's mysterious amulet, and following the old woman's instructions, Cara escapes their pursuer and falls into Luster, the world of the unicorns.
In the center of Luster towers an enormous tree that is the Heart of the World. Now the tree is wounded, pierced by a tunnel that connects it to Earth. Through that tunnel strides Beloved, the ancient enemy of the unicorns, followed by an army of Hunters eager to destroy every last unicorn.
In the third volume of the Unicorn Chronicles, Cara Diana Hunter journeys to the Valley of the Centaurs in quest of a mysterious lost story that could hold the key to the survival of the unicorns.