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 £12,000 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.
Four days later M. Lecoq, the official M. Lecoq, awaited the arrival of Nina Gipsy and Prosper Bertomy. They declared that they had come to meet M. Verduret, who had saved Prosper Bertomy. The detective retired, promising to summon the man they had come to see. A quarter of an hour later M. Verduret entered the room. Facing them, he told them how a friend of his named Caldas had fallen in love with a girl, and how that girl had been won from him by a man who cared nothing for her.
"Caldas determined to revenge himself in his own way. It was his hand that saved the man on the very verge of disgrace. I see you know that you, Nina, are the woman, and you, Prosper, the man; while Caldas is...."
With a quick gesture he removed his wig and whiskers, and the true Lecoq appeared.
"Caldas!" cried Nina.
"No, not Caldas, not Verduret, but Lecoq, the detective."