Sorykah Minuit has a secret that could kill or enslave her: when she is scared or sad, she can change into a man. However, Sorykah is not in control of the change and the man Soryk does not have any memories of Sorykah's life. When he changes back to the woman, Sorykah can remember almost nothing about Soryk or his life.

Sorykah is a scholar but took a job on a submarine because she craves anonymity and must feed herself and her twin babies. After months on the job separated from the children, the submarine surfaces to the polar city of Ostara, and Sorykah can finally see her children again. Unfortunately, they and their nanny are not in the city. Worse, she hears that a terrible man called the Collector has kidnapped her children so that he can vivisect them. Even though she is not a soldier, Sorykah is determined to rescue her children from the Collector's terrible castle. In order to do that, she must defy the deadly frozen weather, find her way through the Erun Forest without running into the Wood Beast, and resist the temptations of the House of Pleasure.

For most of her life, Sorykah has lived among normal humans and tried her best to conceal her mutation. She has not had any contact to the other genetically mutated humans, called somatics. In fact, she hates and fears them just as much as normal humans do. But they may be the only ones who are willing to aid her in her quest.

Except for Sorykah, the somatics look like hybrids of humans and animals. One of the point-of-view characters, the woman Dunya, has a dog's snout, ears, and fur. The Collector's main henchman, Meertham, is large and strong, but he looks like a walrus. Sorykah also meets Rava, whose body resembles an octopus; she has to use a wheelchair to move around. Legends tell of how the somatics came about, but apparently they are the results of a genetic mutation. The somatics are generally oppressed, feared, and a used underclass. They are hunted for sport, and in the cities they do the dirty jobs which the normal humans do not want to do.

The book has several point-of-view characters, though most are shown only briefly when the story needs them; otherwise Sorykah carries the bulk of the POV load. The Collector's housemaid, Dunya, is the second-most prominent character. She hates and fears her master yet also has a strange loyalty to him. She knows very little about the world outside the castle because she has spent most of her life there. Despite having received little compassion or friendship in her life, she is herself a compassionate woman who has pity, up to a point, for the unhappy somatics the Collector imprisons in his dungeons.

While Ice Song is about a mother's need to get her children back, it is also about a rich and powerful family whose members are destroying each other in greed and fear. The main theme of the book is confronting and fearing the "Other" in other people, and even inside yourself. The world of Ice Song is as vibrant and lush as the writing that tells of it.