Scales of Gold, by Dorothy Dunnett

Fourth in the series of the adventures of Niccolò, the smart young Flemish merchant who travels fifteenth century in search of wealth and its inevitable political entanglements. This time, a cunning plan to penetrate deep into Africa becomes complicated by a new wrinkle in a long-standing family feud, and extraordinary dynastic and legal manœuvres from Venice to Madeira to Timbuktu. The ground has been well laid, as one of the supporting cast from the first three books was an African ex-slave who turns out to be extremely well-connected back in his homeland.

It's a good book, as they all are, but the portrayal of Timbuktu as a center of culture, learning, commerce and communication is particularly vivid, and directly challenges any perception of pre-colonisation Africa as somehow backward and savage. On the other hand the violence and illness endured by the protagonist and his friends are pretty graphically portrayed as well, so there is a certain squick factor. Still, very much recommended.