Thuvia, Maid of Mars (Barsoom Book 4)

Carthoris of Mars, prince of Helium, has inherited the strength and heroism of his father, John Carter. He has fallen in love with Thuvia, princess of Ptarth, but she is already promised to Kulan Tith, Jeddak of Kaol. On Barsoom—known to humans as Mars—only death can break an engagement. When Thuvia is kidnapped, Carthoris is blamed for her disappearance. As tensions escalate and bring the red planet toward war, Carthoris pursues her captors into Lothar, an ancient land in the untamed south of Barsoom. There he discovers a mysterious alien race capable of conjuring phantom armies through telepathic projection. Carthoris must fight these conjured enemies to rescue Thuvia and prevent planetary war.