"Finger-prints," explained Hepburn. "Greasy finger-prints on the induction pipe of the engine. I spotted them directly we came on board, so I used the double extension of my camera and took a couple of time exposures. The finger-prints are almost certainly those of one of the thieves." "Unless some of the Weymouth fellows touched the pipe," objected Roche. "I don't think so," replied Hepburn. "For one thing they were made by rather a big man, for the actual marks were an inch and one-eighth wide." "If your surmise is a correct one, Alan," said Mr. Armitage, "those negatives ought to be most useful to the police." "That's what I thought, sir," replied the young amateur detective. "Then you had better come ashore with me and see the superintendent," suggested the Scoutmaster. "It is the duty of every citizen to assist the police; but I hope by so doing we don't have to put off our trip across Channel." "Might we have to do that, sir?" asked Roche in awestruck tones. "More than likely," rejoined Mr. Armitage. "Especially if the thieves are arrested. The police will certainly call us, or some of us, as witnesses. Now, then I'm going ashore to interview the harbourmaster and find out the owner of the motor-yacht who supplied the thieves with petrol in exchange for our compass. One hand will have to remain on board. The others can have leave till eleven o'clock." Mr. Armitage's task was accomplished quicker than he had anticipated. Inquiries resulted in the information that the holder of the _Olivette's_ compass was a well-known yachtsman, who, upon hearing the circumstances under which he had befriended the two thieves, handed back the gear without hesitation. At the police-station the Scoutmaster had to sign a statement, and when he produced the negatives of the finger-prints, the station-sergeant positively beamed with satisfaction. "These ought to work the trick, sir," he remarked. "Scotland Yard will no doubt be able to identify the criminals. It's my belief that they are not fishermen but cracksmen well known to the Yard. You'll hear from us before very long, sir, I don't doubt." Mr. Armitage made no audible comment. Personally he was not at all anxious to have to spoil his lads' holiday by attending police courts and the assizes. Mentally he decided to hurry up matters as far as the Paris trip was concerned, since there were witnesses sufficient to prove the culprits' guilt without the Sea Scouts being called upon to give evidence. At noon the _Olivette_ cast off and proceeded on the last stage of her homeward voyage. It was now blowing steadily from the sou'-west'ard, and with a fair tide outside the harbour the run seemed likely to be quickly performed. With the last of the ebb the _Olivette_ made short work of the distance between Poole Quay and the Bar Buoy; then starboarding helm, shaped a course to pass a mile to the south'ard of Christchurch Ledge.