Middle-aged Zuza starts a new relationship with Kuba. With him, his six-year-old son, Franek, enters her life. Whether she likes it or not, Zuza becomes the boy's foster mother. A unique bond develops, but trouble arises when her relationship with Kuba starts to fall apart. "Stepmother" is an intimate story about love that transcends traditional family roles, the right to one's emotions, and how the most unexpected choices prove to be the right ones.