Eighteen-year-old Aihui Ying dreams of becoming a world-class engineer like her father, but after his sudden murder, her life falls apart. Left with only a journal of her father’s engineering secrets and a jade pendant snatched from the assassin, a heartbroken Ying follows the trail to the capital and the prestigious Engineers Guild — a place that harbors her father’s hidden past — determined to discover why anyone would threaten a man who ultimately chose a quiet life over fame and fortune.

Disguised as her brother, Ying manages to infiltrate the guild’s male-only apprenticeship trial with the help of an unlikely ally—Aogiya Ye-yang, the taciturn eighth prince of the High Command. With her father’s renown placing a target firmly on her back, Ying must stay one step ahead of her fellow competitors, the jealous guild masters, and the killer still hunting for her father’s journal. Complicating everything is her increasingly tangled relationship with the prince, who may have mysterious plans of his own.

The secrets concealed within the guild can be as deadly as the weapons they build and with her life and the future of her homeland at stake, Ying doesn’t know who to trust. Can she avenge her father even if it means going against everything he stood for, or will she be next in the mastermind’s line of fire?