The same steamer which took down the operator and two detectives. brought back one of the same detectives and a negro. This negro, taken to Colonel Baker's office, stated so positively that he had seen Booth and another man cross the Potomac in a fishing boat, while he was looking down upon them from a bank, that the colonel, was at first skeptical; but when examined the negro answered so readily and intelligently, recognizing the men from the photographs, that Baker knew at last that he had the true scent. Straightway he sent to General Hancock for twenty-five men, and while the order was going, drew down his coast survey-maps. With that quick detective intuition amounting almost to inspiration, he cast upon the probable route and destination of the refugees, as well as the point where he would soonest strike them. Booth, he knew, would not keep along the coast, with frequent deep rivers to cross, nor, indeed, in any direction east of Richmond, where he was liable at any time to cross our lines of occupation; nor, being lame, could he ride on; horseback, so as to place himself very far westward of his point of debarkation in Virginia. But he would travel in a direct course from Bluff point, where he crossed to Eastern Tennessee, and this would take him through Port Royal on the Rappahannock river, in time to be intercepted there by the outgoing cavalry men. When, therefore, twenty-five men, under one Lieutenant Dougherty, arrived at his office door, Baker placed the whole under control of his former lieutenant-colonel, E. J. Conger, and of his cousin, Lieutenant L. B. Baker--the first of Ohio, the last of New-York--and bade them go with all dispatch to Belle Plain on the Lower Potomac, there to disembark, and scour the country faithfully around Port Royal, but not to return unless they captured their men. Conger is a short, decided, indomitable, courageous fellow, provincial in his manners, but fully understanding his business, and collected as a housewife on Sunday. Young Baker is large and fine-looking--a soldier, but no policeman--and he deferred to Conger, very properly, during most of the events succeeding. Quitting Washington at 2 o'clock P. M. on Monday, the detectives and cavalrymen disembarked at Belle Plain, on the border of Stafford county, at 10 o'clock, in the darkness. Belle Plain is simply the nearest landing to Fredericksburg, seventy miles from Washington city, and located upon Potomac creek. It is a wharf and warehouse merely, and here the steamer John S. Ide stopped and made fast, while the party galloped off in the darkness. Conger and Baker kept ahead, riding up to farm-houses and questioning the inmates, pretending to be in search of the Maryland gentlemen belonging to the party. But nobody had seen the parties described, and, after a futile ride on the Fredericksburg road, they turned shortly to the east, and kept up their baffled inquiries all the way to Port Conway, on the Rappahannock.