Aissatou's husband, Mawdo, is of very high social standing. He hails from the Senegalese nobility, which means that he's much higher up the social ladder than his first wife.

Even so, Mawdo is still very much in love with his wife despite the enormous social gulf between them. But Mawdo's mother, Aunty Nabou, is not in the least bit pleased with this. She's positively scandalized that her son should fall in love with and marry someone from such a relatively humble background. She cannot and will not accept Aissatou as her daughter-in-law.

So she goes to remarkable lengths to get Mawdo to atone for what she sees as his mistake in marrying Aissatou by taking a second wife, a wife from the same class as himself. The woman she has in mind is her namesake Nabou, Mawdo's cousin.

Mawdo doesn't love Nabou but reluctantly agrees to marry her anyway after his mother, in what is a fairly blatant attempt at emotional blackmail, claims that she will die of shame if he doesn't go through with the marriage. In the conflict between love and duty, duty has clearly won out. In the event, this will lead to the breakdown of Mawdo's marriage to Aissatou.