Jiang Yuan, the illegitimate daughter of the Marquis of Dingyuan's household, is sent to the imperial mausoleum to accompany Helan Cui, a deposed prince. In the seemingly hopeless underground palace, the two see through the layers of traps laid by the imperial court and form a secret alliance. With her exceptional intelligence and strategic skills, she makes her way back to the capital, carefully dismantling family power struggles and investigating a long-buried injustice involving an old border case. From strangers who initially test each other to confidants willing to share life and death, they join hands amid political intrigue to restore order and protect peace across the realm.