Thad, astonished at Bill’s sudden mirth, held the crutch mid-air, and demanded with a malignant leer: 

“Huh!  Laugh, will you?”

“Go ahead and break it, but it won’t be a circumstance to what I’ll do to you.  I can imagine your uncle—­”

“So?  Listen, you pusillanimous, knock-kneed shrimp?  I’m going to mash your jaw so you’ll never wag it again!  And right now, too, you—­”

Possibly there was as much determination back of this as any evil intent, but it also was doomed to failure.  There was a quick step from the deeper shadows and a figure loomed suddenly in front of Thad who, with uplifted crutch, was still glaring at Bill.  Only two words were spoken, a “You, huh?” from the larger chap; then a quick tackle, a short straining scuffle, and Thad was thrown so violently sidewise and hurtled against the bench from which Bill had just risen, that it and Thad went over on the ground together.  The bench and the lad seemed to lie there equally helpless.  Gus picked up the crutch and handed it to his chum.

“Let’s go.  He won’t be able to get up till we’ve gone.”

But as they passed out from among the shadows there followed them a threat which seemed to be bursting with the hatred of a demon: 

“Oh, I’ll get even with you two little devils.  I’ll blow you to—­”

The two boys looked at each other and only laughed.

“Notice his right eye when you see him again,” chuckled Bill.

CHAPTER XVII

THE UNEXPECTED

“Where did you come from, Gus?” Bill asked, still inclined to laugh.

“The road.  Slipped away from the others for I was wondering whether you might not get into trouble.  Couldn’t imagine that chump would spring anything that wouldn’t make you mad, and I knew you’d talk back.  So I did the gumshoe.”

“Well, I suppose he would have made it quite interesting for me and I am eternally grateful to you.  If it weren’t for you, Gus, I guess, I’d have a hard time in—­”

“By cracky, if it weren’t for you, old scout, where would I be?  Nowhere, or anywhere, but never somewhere.”

“That sounds to me something like what Professor Gray calls a paradox,” laughed Bill.

“I don’t suppose you’re going to peach on Thad,” Gus offered.

“No; but wouldn’t I like to?  It’s a rotten shame to have that lowdown scamp under Mr. Hooper’s roof.  It’s a wonder Grace doesn’t give him away; she must know what a piker he is.”

“Bill, it’s really none of our business,” Gus said.  “Well, see you in the morning early.”

The boys wished once more to go over carefully all the completed details of the water power plant; they had left the Pelton wheel flying around with that hissing blow of the water on the paddles and the splashing which made Bill think of a circular log saw in buckwheat-cake batter.  The generator, when thrown in gear, had been running as smoothly as a spinning top; there were no leaks in the pipe or the dam.  But now they found water trickling from a joint that showed the crushing marks of a sledge, the end of the nozzle smashed so that only enough of the stream struck the wheel to turn it, and there was evidence of sand in the generator bearings.