After the French queen gave birth for the fourth time to a stillborn baby, Cardinal Richelieu began to doubt. He decides to open the sarcophagus of one of the four royal infants. The physician Sostain Cantel conducts an examination and declares that the infant was poisoned in the mother’s womb. Richelieu immediately begins a secret investigation to reveal the names of the killers responsible for the deaths of the royal infants. The lead takes him to a robber known by the nickname “Luidor.”