A secret abortion has left Lila, a young Congolese woman, sterile. Her new husband, Minimona, is unhappy with their childless relationship and decides to marry a second wife, Biwa, to bear him children. Biwa quickly produces two children, making her the more "successful" wife by community standards. Lila's jealousy increases, pushing her to invoke the Goddess of Fertility and make a pact that ultimately will have terrible consequences for both women. Meanwhile, Biwa, still young, is not a responsible mother; she is unwilling to give up partying and drinking with her friends every day. She leaves the care of her two children to her co-spouse Lila. Caring for Biwa's children only makes Lila crave children of her own even more. One day, while bathing the baby at the river, Lila hears the older child screaming as she falls from a tree. Horrified, Lila's instinctive reaction is to rush to help, but by doing so, she leaves the baby in the water. At the foot of the tree, the child dies, and the baby, left behind, drowns. To avoid facing the wrath of her rival, Lila runs away and finds refuge in a society of outcast women. But the day soon arrives when Biwa finds Lila and asks the community for justice. The outcast elder, Mfumu Nzonzi, agrees to a death-penalty trial on the condition that both women, not just Lila, are to be judged.
At its core, Luzimbu exposes women's hopes and fears and lays bare the consequences of judgments based on traditional morals. Do both of the women share responsibility for the childrens' deaths? Lila was the one on duty when the children died, but Biwa is their real mother and therefore the one ultimately responsible for their well-being. The outcome of the trial, and what follows afterwards, are based on traditional Congolese morality and a complex spiritual value system overlayed by the often tragic and brutal experiences suffered by the women. Who is judged guilty, and by whom?