Sprague listened, nodded, and rose to join the office-closing retreat.
“That is about what I thought, Archer,” he said soberly. “Now I have one more little job for you, and when it is done we’ll call it a go for to-night. Come around to my laboratory with me and I’ll explain it to you.” And when the four of them reached the plaza-fronting street he excused himself to Maxwell and the chief clerk and went, with Tarbell at his elbow, to the little second-floor den in the Kinzie Building where his experiments in soil analysis were conducted.
Reaching the back room which served as the laboratory proper, Sprague provided his follower with half a dozen small bottles, empty and tightly corked.
“There you are,” he said, from which it may be inferred that the nature of the remaining “job” had been explained on the way up from the railroad head-quarters. “Do it neatly, Archer, and don’t let them catch you at it. Everything will have quieted down by this time, and you shouldn’t have any trouble. I’ll wait for you here.”
Tarbell was gone possibly half an hour, and when he returned the bottles they were filled, two of them with a black-brown liquid, thick and viscous, and four with what appeared to be specimens of more or less dirty water. Each bottle was carefully marked on the blank label pasted upon it. Sprague stood them in a row on the laboratory working-table.
“I shall be busy here for twenty or thirty minutes,” he said. “I don’t want to ride a willing horse to death, but I’d be glad if you’d go by the hotel and ask Mr. Maxwell to wait up for me. I want to see him before he goes to bed.”
Tarbell nodded, but he hesitated about going.
“I got a hunch that we ain’t doin’ all the shadow work by our little lonesomes, Mr. Sprague,” he ventured to say. But before he could go on, Sprague lifted a finger for silence, made a whirling half-turn with a swiftness marvellous in so huge a body, and flung himself through the open door into the unlighted outer office-room to which the laboratory was an inner extension.
There were sounds of a collision, a fall, and a brief struggle before Tarbell could get action. At the end of it Sprague came back into the lighted laboratory, dragging a thick-set, square-shouldered man in pepper-and-salt clothes; a man with a clean-shaven red face down the side of which a thin line of blood was trickling.
“You were eminently correct, Archer,” said the expert, slamming his unresisting burden into a corner of the room after he had deftly gone through the pepper-and-salt pockets for weapons with the result of turning out a cheap revolver and a wicked-looking knife. “I’m sorry I can’t keep my word and let you go to bed, but the plot has thickened a little too rapidly. Go around to the Topaz and ask Mr. Maxwell to wait. Then come back here and keep this fellow quiet while I do my work.”