So Long a Letter recounts two different paths taken by Senegalese women whose choices are extremely limited. The novel discusses the stories of lifelong friends Ramatoulaye (who is writing the letter) and Aissatou and the ways that their relationships with men are both similar and different.

Ramatoulaye ends up marrying Moudou Fall, who eventually becomes enamoured with their daughter's young friend Binetou. Moudou takes Binetou as his second wife, and Ramatoulaye is forced to choose divorce or living as a co-wife. Ramatoulaye decides to stay with Moudou, and she explains in her letter how she finds a way of surviving, working, and raising her children in this difficult situation.

Aissatou, on the other hand, marries Mawdo. Mawdo eventually gives in to pressure from his family to take a second wife. Contrasting with Ramatoulaye's decision, Aissatou divorces her husband, refusing to take part in this oppressive patriarchal tradition of co-wives. 

Binetou, Moudou's second wife, also has a interesting and important story in this book. We learn that Binetou comes from an extremely poor family, and that, because her family needs the financial support, she also has little choice in marrying Moudou.

The novel ends with Ramatoulaye reflecting on modernity and the changing world. She reflects on how her children's paths are even more complicated, and perhaps even more hopeful, than hers and Aissatou's. Ultimately, So Long a Letter is about women living in a world transitioning between old religious cultures and the new cultures of globalization and feminism.

So Long A Letter, a work of fiction by Mariama Ba, is set in Dakar, Senegal, where the main character Ramatoulaye writes a letter to her friend, Aissatou, who lives in America. Although Ramatoulaye is a school teacher in Senegal, she is homebound for four months and ten days after her husband dies, as is the custom in her country.

Through the letter the main character conveys her concerns about the inequalities between men and women in their society. The two women grew up in an era when women were attempting to gain their equality in society in a newly global setting. She reminisces about how the women were influenced by this upbringing as she remained in Senegal, which was gaining its own independence, and how her friend left for America. This one letter encompasses the many trials and tribulations that the women experienced through marriage, betrayal, and the deaths of spouses. Ultimately, the letter addresses the inequalities that face women in African, Islam, and Senegalese societies.