International audience The lies of memory: the reader’s part in Le Cavalier et son ombre by Boubacar Boris Diop and L'Aîné des orphelins by Tierno MonenemboLies are situated at the very core of the narrative structure in both Le Cavalier et son ombre (The Rider and His Shadow) by Senegalese Boubacar Boris Diop and in L’Aîné des orphelins (The Oldest Orphan) by Guinean Tierno Monenembo, two novels dealing with genocide, partly for the first one and chiefly for the second one. This outward paradox eventually reveals the heuristic function of fiction, as it calls for a specific reading capacity, appealing to the reader so that he/she answers to and for it, as philosopher Paul Ricœur says.Differing from historical accounts, narrative fiction is as a matter of fact able to explain the dislocation of time, of conscience and of the world order following a catastrophe. Moreover, the enunciative devices used in each of the two novels demonstrate how the event, which always remains unspeakable, infringes on the very order of the symbolic, thus requiring what Abdourahman A. Waberi called instituting proceedings against the power of language. That is why resorting to unreliable narrators finally refers to the responsibility of a universal reader, established as a witness in each story.