The prison ship of the exiled Cabal Emperor Calus has returned. But its reappearance heralds the beginning of the end as the once-dormant lunar Pyramid stirs to life once more. With the aid of Eris Morn's witchcraft, the Guardian must work with Empress Caiatl, Commander Zavala, and Crow to unravel the mysteries of the Leviathan and the lunar Pyramid and stop Calus before it is too late.