In a world invaded by demons, one girl faces the ultimate test when she is forced to enter an ancient, deadly competition for the chance to save her mother's soul. Nine years ago, the war between the Kingdom of Night and the Kingdom of Rivers tore An'ying's family apart, leaving her mother barely alive and a baby sister to fend for. Now the mortal realm is falling into eternal night, and mó—beautiful, ravenous demons—roam the land, feasting on the flesh of humans and drinking their souls.

An'ying is no longer a helpless child. Armed with her crescent blades and trained in the ancient art of practitioning, she has decided to enter the Immortality Trials, which are open to any mortal who can survive the journey to the immortal realm. Those who complete the Trials are granted a pill of eternal life—the one thing An'ying knows can heal her dying mother. But to attain the prize, she must survive the competition. Death is common in the Trials, yet An'ying finds that a rival contestant is helping her stay alive. Powerful and secretive, Yù'chén is as mysterious about his past as he is about his motives for protecting her. As the competition progresses, it becomes clear that all is not right in the immortal realm. To save her mother and herself, An'ying must determine if she can truly trust the stranger she is falling for, or if he is the most dangerous player of all for herself and for all the realms.