Years after, the Count Louis de Clameron, who had inherited and ruined the estates of which his brother Gaston had been deprived, discovered this secret from the nurse, and finding on inquiries in London that the child had died, persuaded a young ne’er-do-well Englishman to play the role of his brother’s son.  He secretly introduced him to Madame Fauvel, and through this means obtained what money he required from the unhappy woman, who feared the discovery of her past secret by her husband.  The situation was complicated by the count falling in love with Madeline and the sudden appearance of Gaston de Clameron, who was thought to be dead.

The count poisoned his brother, and then, finding that Madeline refused to give up Bertomy, determined to accomplish the cashier’s ruin, and at the same time obtain an amount of money large enough to buy off his fellow-conspirator Lagors.  Lagors, having learnt by chance the password that guarded the safe, was sent to Madame Fauvel late at night with a request for money.

At this time Madame Fauvel was at the end of her resources.  Lagors suggested taking the money from the safe.  Tom between a desire to help her supposed son and the risk of discovery, she at last consented.  Taking M. Fauvel’s key, they descended silently to the safe-room.  At the last moment, just as the key was in the lock, Madame Fauvel attempted to deter Lagors from his purpose.  In the struggle that scratch was made on the door which formed the basis of Lecoq’s inquiries and enabled the great detective to unravel the mystery.

Madeline, who all the while half guessed at the truth, and perceived without being told that Madame Fauvel was at the mercy of the count, had been prepared to sacrifice her future happiness in order to prevent the scandal being made public.

M. Lecoq, armed with these facts, sought out Lagors.  He arrived only in time to prevent a tragedy.  Warned by an anonymous letter that his wife had pawned her diamonds for the benefit of Lagors, the banker came upon them when they were together in Lagor’s rooms.  Imagining the young man was his wife’s lover, the banker drew a revolver and fired four times.  Fortunately, none of the shots took effect, and before he could fire again Lecoq had rushed into the room and torn the weapon from his grasp.  It was the moment of the great detective’s triumph.  With the dramatic skill of which he was a master, he laid bare the whole story and disclosed the true identity of Raoul Lagors.  Before he left he compelled Lagors to refund the L12,000 he had stolen, and in order to avoid a scandal allowed the young man to go free.  Then, that nothing should be wanting to his triumph, he obtained the consent of the banker to Bertomy’s marriage with Madeline.

Hurrying from the banker’s house, Lecoq hastened to effect the arrest of the count.  He arrived too late.  Realising that he was hopelessly in the toils, the count was bereft of his senses and become a hopeless maniac.