"This is no bluff!" he exclaimed. "It's on the level. I have nary doubt but I can find out what's the matter with the critter in five minutes, and if I don't give yer a square deal I don't want a cent for my services, that's all." He would have lifted one of Nemo's feet, but Frank cried: "Drop that! I tell you I don't want you, and I won't have you! Get away from this horse!" The man growled and stiffened up. "All right," he said, somewhat savagely. "I did think of trying to buy the critter off yer, but you're too flip. If the animal stays lame, don't blame me." Although Frank had seemed to pay very little attention to the stranger, he was inspecting him closely. He saw the man had pulled his hat down over his eyes, and wore his coat collar turned up. He had a black beard that concealed his features to a great extent. Grody was also looking the stranger over closely. He fancied he detected a familiar sound in the man's voice. The light in the stable was rather dim, and that served to make the inspection of the boy and the hostler rather unsatisfactory. All at once, Grody started as if struck by a sudden idea. As soon as possible, he whispered in Frank's ear: "That mug is the same chap that were here this afternoon, sir." "The same chap? What chap?" "The one what gave his name as Diamond." "No? You said that fellow had no beard." "I don't believe this man's beard is all right." Frank was aroused. He fancied that he saw a ray of light. The fellow who had called himself Professor Colbath turned away. He had heard the hostler whisper, and he caught Frank's question. Immediately he showed a desire to get out. Leaving the horse to Grody, Frank quickly placed himself before the stranger, saying: "Hold on a minute. I don't know but I'll talk with you a little." "No, yer won't!" growled the man. "I'm done tryin' to talk with a fresh youngster like you--I'm done with you." "Well, I am not done with you!" Frank's voice rang out sharp and stern. "What do you want?" asked the man, uneasily. "I want to see your face." "Well, look at it, and when ye've seen it I'll proceed to smash yours! I don't take no insolence from a kid!" "Take off your hat!" "I will--nit!" "And that beard--take it off!" "Ye're crazy!" cried the man, as he started back. "Am I?" Frank gave a spring and a grab with both hands. One hand snatched away the cap, and the other tore off the black beard, which, indeed, proved to be false. The man uttered an exclamation of rage, and struck at Frank, who dodged the blow. "Is this the fellow, Grody?" cried Frank. "The same mug!" declared the hostler, excitedly. "Well, that's all I want to know!" burst from Frank, as he flung the hat and beard to the floor. "So you were monkeying around my horse to-day, you fakir! Well, what you need is a pair of good black eyes, and I propose to give them to you!" Snap!--off came the boy's jacket in a twinkling, and he still stood between the unmasked man and the door.