Winterstrike spy Hestia Mar has been sent to Caud to recover details of an ancient weapon. During her stay in the Martian city, she encounters the ghost of a warrior, who turns out to be the encoded representation of the city's bombed library. She downloads the data contained here, and the details of the weapon are among them. But Hestia Mar realises too late what she has done: by accessing the data, she has virtually guaranteed the use of the weapon against Caud by her own government. Desperate to rescue the situation she makes her way back home across the dangers of the Crater Plain.
Meanwhile, in Winterstrike itself, the festival of Ombre has been taking place upon the eve of war. Shorn, a woman imprisoned by her family for accidentally consorting with a male - manages to escape. Her sister Essgui follows Shorn and sets out across the Crater Plain where she meets Hestia Mar. Their journey - to recover lost sister and missing weapon - takes them into the dangerous mountains of Mars, and the discovery of a group of outcast male creatures who hold the secrets to the Martian past, and to its future . . .