The full danger of a "hold-up" the boy did not realize. He remembered, however, having read of such occurrences out West where passengers were terrorized and robbed of money and jewelry. But his speculation was again interrupted by the renewal of the conversation. "That will sure set us even, but when can we do it?" inquired a voice eagerly. "And get away safely?" added another. "There's only one place," responded the voice of the man who had suggested the plot. "Where?" chorused the others. "On this end of the long bridge across the river." "Right you are, 'Bo. We can make our 'get-away' down the bank and find some of the 'shanty men' to take us across." "And into the arms of the police," sneered the ringleader. "We'll use the bank to escape, but we won't ask any favors of a 'shanty man'." "Will there be enough money aboard to make it worth while?" inquired one of the schemers, with an evidently practical turn of mind. "Sure; Number 4 always carries a bunch of gold for Western towns." "But how'll we board her?" asked still another. "Get a lantern and wave it." "Will they stop?" "Say, why do you suppose I chose the approach to the bridge?" snapped the man who had proposed the scheme. And then, without giving his companions a chance to speak, he answered his question himself: "Because the engineer'll think there is something wrong on the bridge and stop. It'll be dead easy." Bob's eyes were almost popping out of his head, as, afraid to peep over the top of the car, he stared at the boards as though striving to see through them. Straining his ears to catch every word, he heard another of the plotters begin to speak, when a train thundered past, effectually cutting off all conversation with its roar. Though Bob did not know it, so absorbed was he in listening, less than five minutes had passed since he had started back for the caboose. With the necessity of making a quick shift to the siding, the conductor of the freight train had momentarily forgotten the presence of his youthful charge, and when at last he did remember, it was with the supposition that he had remained in the cab with the engineer. Accordingly, upon receipt of orders to proceed, Hosmer decided to let Bob ride longer in the cab, and shouted to his men to get aboard, waving his arm in the "go ahead" signal to the engineer. But Bob had heard the shouts, and divining their meaning, jumped to the track, having no relish for riding farther in his dangerous position between the cars. Fortunately, both the engineer and conductor saw the boy, as he leaped to the ground, and the signal to start was not obeyed. Recovering his balance, Bob ran toward Hosmer. As he drew near enough for the conductor to see his white, excited face, he exclaimed: "Where have you been? I thought you were in the cab with Barney." "I--I tried to go back over the cars," stammered Bob. "Barney shouldn't have let you. It's too dangerous for a greenhorn."