Feng Wei and Mo Yihang have been in love for nearly three years and are about to get married. Suddenly receiving an inexplicable text message with the tail number 371, Feng Wei ran into what happened between her boyfriend Mo Yihang and her good friend Qi Lu behind Feng Wei's back. Feng Wei overheard that her good friend Qi Lu was pregnant, and Qi Lu's child turned out to be Mo Yihang's. Later, taking into account her boyfriend's betrayal and the morality of not wanting to lose her friend. Qi Lu decided to let Mo Yihang go and let Mo Yihang take good care of Qi Lu, but things were not as simple as Feng Wei thought. Under the unintentional reminder of her good friend Yang Li, Feng Wei looked for clues that exposed the doubts, and investigated bit by bit. The truth behind the matter was beyond her acceptance range.