At Sea: No Mar is a film about Cecília, the only teacher on a small fishing island. One fateful morning Cecília's daughter Maria asks her best friend Lúcia to cover for her as she goes to the beach to watch her father's boat come in. She never returns. Cecília struggles to deal with the guilt of her daughters death and attempts to embrace the impoverished Lúcia. Lúcia's own struggle with her friends death and eventual confession, forces Cecília to reconcile with her own grief and loss.