The seventeenth century arrives. Louis XIV. burns the book in which a person unknown reveals the truth. Captain de Larbeyrie masters a copy, profits by the secret thus obtained, steals a certain number of jewels and dies by the hand of highway murderers. Now at which spot is the ambush laid? At Gaillon! At Gaillon, a little town on the road leading from Havre, Rouen or Dieppe to Paris! A year later, Louis XIV. buys a domain and builds the Château de l’Aiguille. Where does he select his site? In the Midlands of France, with the result that the curious are thrown off the scent and do not hunt about in Normandy. Rouen, Dieppe, the Havre—the Cauchois triangle—everything lies there. On one side, the sea; on another, the Seine: on the third, the two valleys that lead from Rouen to Dieppe. A light flashed across Beautrelet’s mind. That extent of ground, that country of the high tablelands which run from the cliffs of the Seine to the cliffs of the Channel almost invariably constituted the field of operations of Arsène Lupin. For ten years, it was just this district which he parcelled out for his purposes, as though he had his haunt in the very centre of the region with which, the legend of the Hollow Needle was most closely connected. The affair of Baron Cahorn?[3] Or the banks of the Seine, between Rouen and the Havre. [3] _The Seven of Hearts_, by Maurice Leblanc. II; _Arsène Lupin in Prison._ The Thibermenil case?[4] At the other end of the tableland, between Rouen and Dieppe. [4] _The Seven of Hearts_. IX: _Holmlock Shears Arrives Too Late_. The Gruchet, Montigny, Crasville burglaries? In the midst of the Caux country. Where was Lupin going when he was attacked and bound hand and foot, in his compartment by Pierre Onfrey, the Auteuil murderer?[5] To Rouen. [5] _The Seven of Hearts_. IV: _The Mysterious Railway-passenger_. Where was Holmlock Shears, Lupin’s prisoner, put on board ship?[6] Near the Havre. [6] _Arsène Lupin versus Holmlock Shears_, by Maurice Leblanc, Chapter V: _Kidnapped_. And what was the scene of the whole of the present tragedy? Ambrumésy, on the road between the Havre and Dieppe. Rouen, Dieppe, the Havre: always the Cauchois triangle. And so, a few years earlier, possessing the pamphlet and knowing the hiding-place in which Marie Antoinette had concealed the document, Arsène Lupin had ended by laying his hand on the famous book of hours. Once in possession of the document, he took the field, “found” and settled down as in a conquered country. Beautrelet took the field. He set out in genuine excitement, thinking of the same journey which Lupin had taken, of the same hopes with which he must have throbbed when he thus went in search of the tremendous secret which was to arm him with so great a power. Would his, Beautrelet’s efforts have the same victorious results?