Ghost Knocking on the Door

When I was young, my grandma often told me that there are good and evil in people's hearts, and that ghosts can distinguish between turbid and pure. Later, after my grandfather took my eldest and second uncle out to find my father but never came back, grandma never said this again. I thought I was like ordinary people, living an ordinary life step by step, until that night, I saw a ghost knocking on the door.