"So Long a Letter" is an epistolary novel that explores the life of a recently widowed woman in Senegal. Throughout the story, she reflects on her life, her marriage, her husband's second, younger wife, and the status of women in Senegalese society. The book delves into themes of polygamy, friendship, and the struggle for women's rights in a predominantly patriarchal society. It is a poignant examination of the personal and cultural conflicts faced by women in post-colonial Africa.

The novel revolves around the tragic story of a young Antillean woman who, through her diary entries, reveals the harrowing details of her life and marriage. After moving to Africa to be with her new husband, she finds herself isolated and trapped in a world of deception and disillusionment. Her husband's indifference and infidelity, coupled with her growing sense of alienation in a foreign land, lead her down a path of despair. The narrative unfolds as her diary is read by another woman, who empathizes with her struggles and reflects on the complexities of identity, belonging, and the painful legacy of colonialism.