From the back cover:
"Legends speak of a time before history, of a great island empire whose people wielded powerful magic and technology, ruling much of the world. Their pride proved their undoing, and Atlantis sank beneath the sea in a single night.
Twilight of Atlantis is a sourcebook detailing this once-great people, drawn from the writings of Plato. New races such as the Bastai cat-warriors and the Atlanteans appear, new prestige classes (Artificer, Orphean, Resonant, Spellbane) and six new feats to use with them. A whole new approach to magic - that of the resonance, powered by the mystical metal orichalcum - is provided, with 10 new spells. Join the adventure today, attempting to overthrow or rescue Atlantis' great empire."