Lin Xuan, a thousand-year-old mystical serpent, enters the Xiao General's household as a live-in son-in-law for five years to repay a life-saving debt from a previous existence. Using his demonic powers in secret, he protects the female general Xiao Luan and helps her rise from obscurity to become the General Who Guards the North. Yet Xiao Luan mistakenly believes that the refugee Shen Yu is her savior and subjects Lin Xuan to endless humiliation. When the truth finally comes to light, Lin Xuan transforms into a dragon and leaves. Xiao Luan loses the support of everyone around her, is stripped of her military rank, and reduced to an ordinary citizen. Only then does she discover that all her military achievements over the past five years were secretly orchestrated by him. She kneels three times at Yuxu Temple, begging him to return, but he leaves her with only one sentence: their karmic debt is settled. In the end, Lin Xuan cultivates into a Yinglong and ascends to the heavens, while Xiao Luan grows old in a secluded courtyard, clutching the remains of their marriage contract and regretting half her life until her dying breath.