The heroine is a trainee at the Matchmaking Office in the Immortal Realm. After tying the wrong red threads between two brothers, her master sends her down to the human world to cut them apart. While doing so, she accidentally connects the older brother's red thread to herself.
Her master in the Immortal Realm orders her to cut the thread connecting her to the hero and help the younger brother find his destined love.
The heroine seeks help from her second senior brother, Lang Mu, who was banished to the mortal realm twelve years ago for tying a red thread between two men. She learns that the only way to sever the red thread between an immortal and a mortal is to tie countless red threads onto the hero.
During her conversations with Lang Mu, the heroine realizes that love isn't something that can arise only between a man and a woman. So she defies her master's orders and helps Lang Mu and the younger brother get together.
To help the heroine return to the Immortal Realm as soon as possible, her eldest senior brother pretends to be her boyfriend to make the hero jealous, and arranges for the hero's idealized first love to return from abroad.
But the idealized first love is ruthless. She kidnaps the heroine and forces her to leave the hero. In the end, the hero arrives in time to save the heroine and severs the red thread on his own body.
