|To find his father, a teenager called Yan Liang escapes from the orphanage with his “sister” Pupu and returns to Ning City. They live in his childhood friend Zhu Chaoyang’s home. When the three children play, they shoot a video of Zhang Dongsheng killing someone. They are afraid if they call the police, they will be sent back to the orphanage, so the three children decide to write a letter to warn the murderer not to kill people again. But Zhang Dongsheng comes to them. Therefore, there comes a thrilling battle between the three children and the murderer.