Twenty days before the wedding, Su Wan follows her fiancé He Chen and his group into the mountains for camping. Through a draw, He Chen and his childhood sweetheart Qin Shu are assigned a double tent, while Su Wan is left with only a crude single moisture-proof mat. On a rainy night when the tent leaks, she slowly begins to see the truth: everyone favors Qin Shu, an old tree has their youthful names carved on it, and she is merely a substitute for Qin Shu during her time abroad.