But there was enough to expose the whole plan of smuggling a huge amount of diamonds into the United States. The Bradys were astonished and Harry said at once: "This letter proves that La Croix must be the gigantic smuggler whom the Customs department want run down." "No question about it," replied Old King Brady. "And as we have the details of a scheme he intends to operate, we had better make preparations to nip the plan in the bud, or else to capture the girl smuggler when she makes her attempt to beat the Custom House." "Are you aware that the steamer Champagne sails for Havre to-day?" "Does she?" muttered Old King Brady, glancing at his watch. "Well, we'll barely have time to reach her if we go at once. Get a cab and we'll see if we can catch her before she departs." "Even if we miss her," said Harry, consolingly, "we will be pretty sure to see La Croix on the pier, seeing his daughter off." "I don't want to arrest him in that case," said Old King Brady, "for if the girl gets away, we'll have to keep the man watched in order to let him lead us to his daughter when she returns. As she's pretty sure to have all those diamonds with her, we can nab them with evidence on their persons, of their smuggling enterprise." Harry nodded and they hurried out together. A hack was engaged and they rode over to the French Trans-Atlantic Company's pier on the North river. By the time the cab reached the dock, however, the steamship's mooring lines had been cast off, the gangplank was down and the vessel was being pulled out into the stream. The detectives were disappointed. Eagerly scanning the throng of passengers on the upper deck, they suddenly caught view of Clara La Croix. The girl was standing in the stern waving her handkerchief and shouting to a stylishly-dressed middle-aged woman on the stringpiece: "Good-by, mamma!" "Farewell, Clara--be very careful of yourself, my child!" replied the woman, as she waved her handkerchief back at the girl. Harry nudged Old King Brady. "There's her mother," he muttered, "but La Croix has not shown up. He fears arrest now, as he knows we are after him." "So much the better," replied the old detective, drily. "This woman won't know us. It will therefore be all the easier to follow her undetected." The steamship soon went down the river and the friends and relatives of the departing passengers began to leave the pier. Mrs. La Croix was one of the last to go. She did not know that the Bradys were close behind her. CHAPTER V. AT A VILLAIN'S MERCY. The smuggler's wife leisurely left the pier, crossed the street and went in the direction of Sixth avenue, on foot. It did not seem to occur to her that she might be followed, for she never once glanced back in the direction she came from. Old King Brady and his partner did not know much about the woman. Whether she was actually concerned in La Croix's smuggling games or not, they had not the faintest idea.