Prisonnières is a story set in a women's prison where the inmates arrive for long sentences, some up to eight years. They spend their days making teddy bears under the watchful eye of Dessombes, the head matron who is always on the lookout for any misbehavior.
Intelligence is passed on to Dessombes by Marthe, an older convict who seems to know everything that goes on in the prison. When Nelly is unfairly sent to solitary confinement, the other women suspect Marthe of being involved. This leads to Brigitte ending her friendship with Marthe.
However, Marthe finds solace in Nicole, a prisoner shunned by the others for infanticide. She takes Nicole under her wing, becoming a surrogate mother to her. Meanwhile, Sabine, a young and energetic inmate with a supportive husband, falls in love with Lucie, a woman who has lost hope and fears her release from prison.
As tensions rise among the inmates, Prisonnières explores the complex relationships and dynamics within the women's prison.