From this simple experiment Lecoq deduced that two people were present when the safe was robbed; one wanted to take the money, the other wanted to prevent it being taken.  This was the basis of the case which he set out to draw up against some person or persons unknown.  He argued, with his usual clear logic, that neither Fauvel nor Bertomy could have robbed the safe.  Both of them had keys; both of them knew the secret word and could have robbed the safe whenever they pleased.  Therefore, neither of them would have committed the theft in the presence of somebody else.

II.—­A Mysterious Journey

Lecoq’s first steps after establishing these preliminary deductions was to secure the release of Bertomy on the grounds of insufficient evidence.

On the very morning of his release, Bertomy had received a mysterious letter composed of printed words cut out letter by letter from a book and pasted on paper.

“My dear Prosper,” so the epistle ran, “a friend who knows the horror of your situation sends you this help.  There is one heart at least which feels for you.  Leave France; you are yourself.  The future is before you.  Go, and may this money be of use.”

Enclosed with this note were banknotes for L400.  Lecoq, disguised as a M. Verduret, a country merchant, a friend of Bertomy’s father, secured this epistle and studied it carefully.  His knowledge of the various types used by the printers in Paris showed him that the letters had been taken from a book printed by a well-known firm who published volumes of devotion.  The correctness of this conclusion was established by the discovery on the back of one of the small cuttings the word “Deus.”  The words had been cut from a Catholic prayer-book.  To find that prayer-book was his next business.

In another disguise he sought out Nina Gipsy, and, by asking her assistance to clear Prosper, induced her to take up the position of lady’s-maid in the Fauvel family, for it was there, he conceived, the mutilated book of devotion would be found.  Again his wonderful instinct proved right.  In a few days Nina brought him the very book—­a prayer-book, belonging to Madeline, which had been given her by Bertomy.

Why had Madeline sent the cashier this elaborately disguised letter?  Why had she wished him to leave France, confident as she was, so she told him, of his innocence?

To find an answer to these important queries, Lecoq closely questioned Bertomy.  He learnt that the night before the robbery the cashier had dined with his friend Raoul de Lagors, the wealthy, dissolute young nephew of M. Fauvel’s wife.  This Lagors was the friend of Count Louis de Clameran, whose demand for the L12,000 left him by his dead brother had resulted in the discovery of the mysterious robbery.

Bertomy had nothing but the highest praise for Lagors, but, on the other hand, spoke most disparagingly of the count.  The count, it appeared, had proposed for the hand of Madeline, and had pressed his suit with great determination.  And Madeline—­and this was what provided a new problem for Lecoq’s consideration—­had tacitly accepted his attention.