Four close friends check into a mountain guesthouse to unwind, but a hairpin belonging to a deceased person triggers a chain of suspicions. As a series of bizarre events unfolds, the four gradually reveal the dark sides of their hearts. They accuse one another and bring up old grudges, only to discover that Su Xin has orchestrated the revenge out of long-standing misunderstandings. Once the truth comes to light, the four reconcile and rediscover the true meaning of friendship.