Cassie strikes a bargain with a magical polar bear to be his wife in exchange for his help in finding and freeing her mother from her imprisonment in a troll castle. Cassie is a young researcher who lives at a research station in the Arctic with her dad and his team of scientists. She is committed to researching polar bears in the arctic with her dad. The story begins when she spies a strange polar bear in the arctic desert. After following it for hours, it looks like it disappears through the ice. When Cassie returns to the research station that day and relays her impossible story to her dad, her dad realizes that Cassie is behaving very recklessly as lately she has gone out more often by herself when she should have brought a team or a partner with her for safety. Her dad suggests she enroll at the University of Alaska and live with her Gran in Fairbanks rather than stay with him in such a dangerous place.
When her Gran arrives at the research station the next morning, Cassie learns the strange story of her past. Her Gran tells her the bedtime stories she'd been telling Cassie since she was a little kid - the stories about the Polar Bear King and the lands East of the Sun, West of the Moon - were true! Cassie learns that her mother was the daughter of the North Wind and had made a bargain with the Polar Bear King which resulted in the Polar Bear King coming after Cassie on her eighteenth birthday. Gran tells Cassie that it is imperative that she take Cassie safely away before the Polar Bear King comes to claim his end of the bargain. That evening, Cassie finally encounters the Polar Bear King who is able to speak - a scientific impossibility! Cassie learns that her grandfather, the North Wind was angered that Cassie's mother had eloped with her father. Cassie's mother had engaged the help of the Polar Bear King to hide her, and in exchange Cassie was promised to be the Polar Bear King's wife when she grew of age. Unfortunately, the North Wind found her mother and in his anger blew her to the troll's domain, where she has been imprisoned since. Cassie tells the Polar Bear King that she will marry him if he helps her free her mother. The Polar Bear King agrees and brings Cassie to his beautiful ice palace.
The Polar Bear King who calls himself simply, Bear, tells Cassie that he is a "munaqsri" which is Inupiaq for "guardian". He is a magical being that transports and transfers souls from those who die to newborns to ensure the cycle of life. His particular responsibility is to care for the polar bear souls. Cassie is immensely skeptical of all this new information as she has grown up on the firm foundations of science. On the night after the wedding, Cassie is awakened to find a human shape lying in bed next to her. In her horror, she kicks him out by threatening to hack at him with an axe. The next day, she learns that the human shape was really Bear transformed. Bear explains that munaqsri can change their form and he wants his children to be human. Cassie is appalled that she is treated like a human incubator but Bear tells her he also wants her to love him. He tells Cassie that he will wait until Cassie falls in love with him. Cassie believes she will never fall in love with him as the whole situation is completely absurd and tells Bear that she changed her mind and wants to go home. Bear asks that she give herself some time to adjust and tries to convince her to stay by telling her she can never return to having a normal life after what she has experienced. The next few days Cassie learns that Bear has successfully saved her mother from the troll castle. He promises that Cassie will eventually be able to go home and visit her mother and father. Over the next few weeks Cassie learns more about Bear's life and how he used to be human before he took up the mantle of becoming a munaqsri from his father. Slowly, she becomes more and more comfortable with Bear, despite the strangeness of the entire situation. Eventually, she allows Bear to sleep in the same bed as her, however Bear tells Cassie she must never see his human face and refuses to explain to her why she can't.
One day, Cassie tells Bear that she wants to go home. She has grown to like Bear very much but this new life is not for her. Bear tells Cassie he loves her but brings her back to the research station. There, she meets her mom for the first time and learns that trolls are really wild spirits that have lingered in their spirit form for too long. Cassie throws herself back into the regular research schedule. Over the next few days, she realizes that she misses Bear. Bear often feels wracked with sadness when he is too late to deliver a soul to a newborn polar bear cub as the cub ends up being stillborn. Cassie comes up with an idea to printout a map that has known polar bear denning sites along with data on gestation periods. She tells her parents that she wants to go back to Bear and help him use this information to perform his duties as a munaqsri. Everything thinks she is crazy but she is determined to return.
Bear is ecstatic that she has returned. Together he and Cassie work to perform the munaqsri duties with Cassie's maps and data. Cassie falls more in love with Bear and one night she and Bear sleep together. Cassie soon finds herself pregnant. One night, she gives into temptation and sees Bear's face for the first time while he is sleeping. When Bear awakens he is saddened as he had struck a bargain with the trolls which allowed him to free Cassie' mother in exchange that Cassie will never see his human face or know why she must not. Now, Bear must marry the troll princess. Before Bear is taken away to the troll castle, Cassie promises him she will search the ends of the earth to find him and get him back.
Once Bear is gone, his entire ice palace melts and falls apart. Cassie finds herself alone in the arctic. Suddenly, many polar bears assemble and follow Cassie as she begins her search for Bear. Cassie endures terrifying arctic snow storms and almost dies of hunger and cold. One night, however, she awakens to find herself warmly ensconced by hundreds of polar bears and a female polar bear allows her to suckle some of her milk for sustenance. Cassie eventually meet other munaqsri representing other species in the arctic. They all think her quest is crazy and suggest that she stop searching for Bear and focus on keeping herself and her future child safe. Cassie is so desperate for help, she jumps into the arctic waters to force the munaqsri of the water to help her. Eventually they tell her she should seek help from Father Forest and transport her to his domain on a fast current of water.
Father Forest has a cottage in the woods that border the edge of the Arctic. Father Forest promises Cassie he will help her but only after he attends to his own duties as guardian of the forest. Eventually, Cassie figures out that he never intended to help her find Bear as his agenda was to delay her until she gave birth to her child since munaqsri numbers are falling and newborn munaqsri are in high demand to ensure the continuation of the munaqsri line to take up responsibilities important for the cycle of life. Father Forest traps Cassie in his cottage by getting the trees to wrap their roots around her and prevent her from continuing on her quest. Cassie eventually complies with Father Forest and he allows her to work for him. For the next few months, she bides her time with Father Forest until he drops his guard. One day, Cassie finds her opportunity to escape while Father Forest is distracted with an ailing tree spirit. Cassie jumps into a river which takes her far away. She runs blindly through a forest until she runs right off a cliff where she falls to near death. An Inuit man who turns out to be a munaqsri appears and tells Cassie he must take her soul, as she is too broken to heal. Cassie strikes a bargain with the munaqsri, telling him that she knows where to find thousands of unclaimed souls. The munaqsri is eager to collect these souls as there have been too many stillbirths in the human population. In exchange, the munaqsri heals Cassie and her baby.
The Inuit munaqsri accompanies Cassie on her quest to find the North Wind. Cassie ends up high up in the mountains but she can't get her grandfather's attention no matter how loudly she shouts for his help. A dragon munaqsri tells her the only way to get his attention is by falling through the air. She jumps off the dragon's back as it is flying and is caught by the East, West and South winds who pity her and take her to the North Wind's domain. The North Wind is angry that Cassie dares speak about her mother in his presence. Cassie eventually helps her grandfather the North Wind forgive himself for what he did to her mother in a moment of foolish anger. She tells her grandfather that her mother is alive and safe. Her grandfather helps blow Cassie all the way to the land East of the Sun and West of the Moon where the trolls live.
In the troll's domain, Cassie meets the troll princess. The troll princess tells Cassie she will let her go but Cassie will not be allowed to take Bear with her as Bear is needed to make a troll baby. Cassie tells the troll princess she will help her convince Bear to do the right thing. When the troll Queen finds out Cassie is pregnant, she demands that Cassie give her the child. Cassie refuses and the Queen locks her up until she complies. The troll princess takes pity on her and opens a door for her to escape the palace. Right at that moment, Cassie starts feeling contractions and the baby is about to come out. The Inuit munaqsri helps Cassie give birth, however, there are no human souls here in the land East of the Sun, West of the Moon. Cassie puts two and two together and figures out that troll spirits are actually very old spirits that have lingered on earth for so long they have forgotten their original identities. She tells the troll princess that she has the opportunity to experience life again and allows the troll princess' soul to go into her baby. Eventually, Cassie will help the trolls find new homes inside newborns and be reunited with Bear again.
Best part of story, including ending:
I really loved that Sarah Beth Durst wrote the story with a scientific bent, even though the story is a fairy tale. I thought it was very clever how she melded science and magic together to describe how different species have a munaqsri guardian to care for it and the reason why species are dying out is because there are no munaqsri to take over the duties.
Best scene in story:
My favorite scene was when Cassie returns to Bear with the data on the Polar Bear denning sites. It was a very touching and romantic reunion and it was very heart-warming to see Cassie and Bear working together to nurture newborn polar bears when before Cassie felt very useless living in Bear's ice palace with nothing to do.
Opinion about the main character:
I enjoyed that Cassie has a scientific mind and tries to make sense out of the supernatural events that seem to happen around her. This clash between science and magic often results in humorous dialogue and thought-processes which end up with Cassie getting frustrated or resigning herself to the fact that not everything can be explained by science.