Kamzin has always dreamed of becoming one of the Emperor's royal explorers, the elite climbers tasked with mapping the wintry, mountainous Empire and spying on its enemies. She knows she could be the best in the world, if only someone would give her a chance. But everything changes when the mysterious and eccentric River Shara, the greatest explorer ever known, arrives in her village and demands to hire Kamzin -- not her older sister Lusha, as everyone had expected -- for his next expedition. This is Kamzin's chance to prove herself -- even though River's mission to retrieve a rare talisman for the emperor means climbing Raksha, the tallest and deadliest mountain in the Aryas. Then Lusha sets off on her own mission to Raksha with a rival explorer who is determined to best River, and Kamzin must decide what's most important to her: protecting her sister from the countless perils of the climb or beating her to the summit.