The Tale of the Three Worlds.Tetrarch is the sequel to 'Geomancer', and the second book in the 'Well Of Echoes' trilogy.The Aachim have invaded Santhenar with a fleet of constructs. Blaming humanity for the loss of Aachan, they demand half the world. Humankind, facing defeat by the alien lyrinx, is in no position to resist.Humanity's future rests in the hands of: Tiaan, whose geomancy holds the key to all power; Nish, who has sworn to bring her justice; and Irisis. Tiaan opens the gate to save her beloved, Minis, but he rejects her and she has betrayed her world to the invading Aachim. Now Nish, bent on retribution hunts her through the abandoned city, and there is no way out.