Cyprian Ghezo, crown prince of Dahomey (now Benin), is a student at Sorbonne University. Passionate about history and art, he participates as a worker in the renovation of a historical monument in Paris. This descent into the rubble leads him to the traces of a horrible crime once committed by the Kingdom of France under the Old Regime, and which continues to be kept secret today by the French Republic. The victim was a prince kidnapped from the Kingdom of Dahomey and brought to the court of Louis XIV as a slave. Cyprian's discovery alarms the secret services of the Republic. At first, they try to use discreet methods to prevent the student from reaching the truth. But Cyprian's obsession soon leads him to become a target of a real manhunt in Paris.