Lin Hao has been married for two years, but in bed he only knows how to thrust away, one poke at a time, and has never once brought his wife to orgasm. Late one night, the wife texts her mother: "He's still the same." Her widowed mother, Zhao Yaqin, shows up at their door and says just one thing: "Don't call me Mom—call me Mommy." She starts the lessons from the knees: how to touch with your hands, how to lick with your mouth, how to drive with your hips. Outside the crack in the door, the wife watches her husband being taught for the first time—and finds herself getting wet first; even her younger sister slips a hand under her own skirt. It turns out the mother-in-law isn't sacrificing herself—she's taking a man who doesn't understand her daughter and training him into something that belongs to her.