The little French office clock—Bromley's testimonial from his enthusiastic and admiring classmates of the École Polytechnique—had chimed the hour of ten; the August moon rose high in a firmament of infinite depths above the deserted bunk shanties and the silent machinery on the camp mesa; the big touring car, long since cooled from its racing climb over the hills of the roundabout road, cast a grotesque and fore-shortened shadow like that of a dwarfed band-wagon on the stone-chip whiteness of the cutting yard; and still the members of the auto party lingered on the porch of the adobe bungalow.

For Ballard, though he was playing the part of the unprepared host, the prolonged stay of the Castle-'Cadians was an unalloyed joy. When he had established Mrs. Van Bryck in the big easy-chair, reminiscent of Engineer Macpherson and his canny skill with carpenter's tools, and had dragged out the blanket-covered divan for Miss Cantrell and Bigelow, he was free. And freedom, at that moment, meant the privilege of sitting a little apart on the porch step with Elsa Craigmiles.

For the first time in weeks the Kentuckian was able to invite his soul and to think and speak in terms of comfortable unembarrassment. The long strain of the industrial battle was off, and Mr. Pelham's triumphal beating of drums had been accomplished without loss of life, and with no more serious consequences than a lamed arm for the man who was best able to keep his own counsel. Having definitely determined to send in his resignation in the morning, and thus to avoid any possible entanglement which might arise when the instability of the great dam's foundations should become generally known, the burden of responsibility was immeasurably lightened. And to cap the ecstatic climax in its sentimental part, Elsa's mood was not mocking; it was sympathetic to a heart-mellowing degree.

One thing only sounded a jarring note in the soothing theme. That was young Blacklock's very palpable anxiety and restlessness. When the collegian had placed the big car, and had stopped its motor and extinguished its lights, he had betaken himself to the desert of stone chips, rambling therein aimlessly, but never, as Ballard observed, wandering out of eye-reach of the great gray wall of masonry, of the growing lake in the crooking elbow of the canyon, and the path-girted hillside of the opposite shore. Blacklock's too ostentatious time-killing was the latest of the small mysteries; and when the Kentuckian came to earth long enough to remark it, he fancied that Jerry was waiting for a cue of some kind—waiting and quite obviously watching.

It was some time after Mrs. Van Bryck, plaintively protesting against being kept out so late, had begun to doze in her chair, and Bigelow had fetched wraps from the car wherewith to cloak a shuddery Miss Cantrell, that Ballard's companion said, guardedly: "Don't you think it would be in the nature of a charity to these two behind us if we were to share Jerry's wanderings for a while?"

"I'm not sharing with Jerry—or any other man—just now," Ballard objected. None the less, he rose and strolled with her across the stone yard; and at the foot of the great derrick he pulled out one of the cutter's benches for a seat. "This is better than the porch step," he was saying, when Blacklock got up from behind a rejected thorough-stone a few yards away and called to him.

"Just a minute, Mr. Ballard: I've got a corking big rattler under this rock. Bring a stick, if you can find one."

Ballard found a stick and went to the help of the snake-catcher.

"Don't give him a chance at you, Jerry," he warned. "Where is he?"

The collegian drew him around to the farther side of the great thorough-block.

"It was only a leg-pull," was the low-toned explanation. "I've been trying all evening to get a word with you, and I had to invent the snake. Wingfield says we're all off wrong on the mystery chase—'way off. You're to watch the dam—that's what he told me to tell you; watch it close till he comes down here from Castle 'Cadia."

"Watch the dam?" queried the engineer. "What am I to look for?"

"I don't know another blessed thing about it. But there's something doing; something bigger than—'sh! Miss Elsa's asking about the snake. Cut it out—cut it all out!"

"It was a false alarm," Ballard explained, when he rejoined his companion at the derrick's foot. "Jerry has an aggravated attack of imaginationitis. You were saying——?"

"I wasn't saying anything; but I shall begin now—if you'll sit down. You must be dying to know why we came down here to-night, of all the nights that ever were; and why we are staying so long past our welcome."

"I never felt less like dying since the world began; and you couldn't outstay your welcome if you should try," he answered, out of a full heart. "My opportunities to sit quietly in blissful nearness to you haven't been so frequent that I can afford to spoil this one with foolish queryings about the whys and wherefores."

"Hush!" she broke in imperatively. "You are saying light things again in the very thick of the miseries! Have you forgotten that to-day—a few hours ago—another attempt was made upon your life?"

"No; I haven't forgotten," he admitted.

"Be honest with me," she insisted. "You are not as indifferent as you would like to have me believe. Do you know who made the attempt?"

"Yes." He answered without realising that the single word levelled all the carefully raised barriers of concealment; and when the realisation came, he could have bitten his tongue for its incautious slip.

"Then you doubtless know who is responsible for all the terrible happenings; the—the crimes?"

Denial was useless now, and he said "Yes," again.

"How long have you known this?"

"I have suspected it almost from the first."

She turned upon him like some wild creature at bay.

"Why are you waiting? Why haven't you had him arrested and tried and condemned, like any other common murderer?"

He regarded her gravely, as the hard, white moonlight permitted. No man ever plumbs a woman's heart in its ultimate depths; least of all the heart of the woman he knows best and loves most.

"You seem to overlook the fact that I am his daughter's lover," he said, as if the simple fact settled the matter beyond question.

"And you have never sought for an explanation?—beyond the one which would stamp him as the vilest, the most inhuman of criminals?" she went on, ignoring his reason for condoning the crimes.

"I have; though quite without success, I think—until to-day."

"But to-day?" she questioned, anxiously, eagerly.

He hesitated, picking and choosing among the words. And in the end he merely begged her to help him. "To-day, hope led me over into the valley of a great shadow. Tell me, Elsa, dear: is your father always fully accountable for his actions?"

Her hands were tightly clasped in her lap, and there were tense lines of suffering about the sweet mouth.

"You have guessed the secret—my secret," she said, with the heart-break in her tone. And then: "Oh, you don't know, you can't imagine, what terrible agonies I have endured: and alone, always alone!"

"Tell me," he commanded lovingly. "I have a good right to know."

"The best right of all: the right of a patient and loving friend." She stopped, and then went on in the monotone of despair: "It is in the blood—a dreadful heritage. Do you—do you know how your father died, Breckenridge?"

"Not circumstantially; in an illness, I have been told. I was too young to know anything more than I was told; too young to feel the loss. Did some one tell me it was a fever?"

"It was not a fever," she said sorrowfully. "He was poisoned—by a horrible mistake. My father and his brother Abner were practising physicians in Lexington, your old home and ours; both of them young, ardent and enthusiastic in their profession. Uncle Abner was called to prescribe for your father—his life-long friend—in a trivial sickness. By some frightful mistake, the wrong drug was given and your father died. Poor Uncle Abner paid for it with his reason, and, a few months later, with his own life. And a little while after his brother's death in the asylum, Father threw up his practice and his profession, and came here to bury himself in Arcadia."

The Kentuckian remembered Colonel Craigmiles's sudden seizure at his first sight of the dead Ballard's son, and saw the pointing of it. Nevertheless, he said, soberly: "That proves nothing, you know."

"Nothing of itself, perhaps. But it explains all the fearful things I have seen with my own eyes. Two years ago, after the trouble with Mr. Braithwaite, father seemed to change. He became bitterly vindictive against the Arcadia Company, and at times seemed to put his whole soul into the fight against it. Then the accidents began to happen, and—oh, I can't tell you the dreadful things I have seen, or the more dreadful ones I have suspected! I have watched him—followed him—when he did not suspect it. After dinner, the night you arrived, he left us all on the portico at Castle 'Cadia, telling me that he was obliged to come down here to the mine. Are you listening?"

"You needn't ask that: please go on."

"I thought it very strange; that he would let even a business errand take him away from us on our first evening; and so I—I made an excuse to the others and followed him. Breckenridge, I saw him throw the stone from the top of that cliff—the stone that came so near killing you or Mr. Bromley, or both of you."

There had been a time when he would have tried to convince her that she must doubt the evidence of her own senses; but now it was too late: that milestone had been passed in the first broken sentence of her pitiful confession.

"There was no harm done, that time," he said, groping loyally for the available word of comforting.

"It was God's mercy," she asserted. "But listen again: that other night, when Mr. Bromley was hurt ... After you had gone with the man who came for you, I hurried to find my father, meaning to ask him to send Otto in the little car to see if there was anything we could do. Aunt June said that father was lying down in the library: he was not there. I ran up-stairs. His coat and waistcoat were on the bed, and his mackintosh—the one he always wears when he goes out after sundown—was gone. After a little while he came in, hurriedly, secretly, and he would not believe me when I told him Mr. Bromley was hurt; he seemed to be sure it must be some one else. Then I knew. He had gone out to waylay you on your walk back to the camp, and by some means had mistaken Mr. Bromley for you."

She was in the full flood-tide of the heart-broken confession now, and in sheer pity he tried to stop her.

"Let it all go," he counselled tenderly. "What is done, is done; and now that the work here is also done, there will be no more trouble for you."

"No; I must go on," she insisted. "Since others, who have no right to know, have found out, I must tell you."

"Others?" he queried.

"Yes: Mr. Wingfield, for one. Unlike you, he has not tried to be charitable. He believes——"

"He doesn't love you as I do," Ballard interrupted quickly.

"He doesn't love me at all—that way; it's Dosia. Hadn't you suspected? That was why he joined Aunt Janet's party—to be with Dosia."

"Thus vanishes the final shadow: there is nothing to come between us now," he exulted; and his unhurt arm drew her close.

"Don't!" she shuddered, shrinking away from him. "That is the bitterest drop in the cup of misery. You refuse to think of the awful heritage I should bring you; but I think of it—day and night. When your telegram came from Boston to Mr. Lassley at New York, I was going with the Lassleys—not to Norway, but to Paris, to try to persuade Doctor Perard, the great alienist, to come over and be our guest at Castle 'Cadia. It seemed to be the only remaining hope. But when you telegraphed your changed plans, I knew I couldn't go; I knew I must come home. And in spite of all, he has tried three times to kill you. You know he must be insane; tell me you know it," she pleaded.

"Since it lifts a burden too heavy to be borne, I am very willing to believe it," he rejoined gravely. "I understand quite fully now. And it makes no difference—between us, I mean. You must not let it make a difference. Let the past be past, and let us come back to the present. Where is your father now?"

"After dinner he went with Mr. Wingfield and Otto to the upper canyon. There is a breakwater at the canyon portal which they hoped might save the power-house and laboratory from being undermined by the river, and they were going to strengthen it with bags of sand. I was afraid of what might come afterward—that you might be here alone and unsuspecting. So I persuaded Cousin Janet and the others to make up the car-party."

From where they were sitting at the derrick's foot, the great boom leaned out like a giant's arm uplifted above the canyon lake. With the moon sweeping toward the zenith, the shadow of the huge iron beam was clearly cut on the surface of the water. Ballard's eye had been mechanically marking the line of shadow and its changing position as the water level rose in the Elbow.

"The reservoir is filling a great deal faster than I supposed it would," he said, bearing his companion resolutely away from the painful things.

"There have been storms on the main range all day," was the reply. "Father has a series of electrical signal stations all along the upper canyon. He said at the dinner-table that the rise to-night promises to be greater than any we have ever seen."

Ballard came alive upon the professional side of him with a sudden quickening of the workaday faculties. With the utmost confidence in that part of the great retaining-wall for which he was personally responsible—the superstructure—he had still been hoping that the huge reservoir lake would fill normally; that the dam would not be called upon to take its enormous stresses like an engine starting under a full load. It was for this reason that he had been glad to time the closing of the spillway in August, when the flow of the river was at its minimum. But fate, the persistent ill-fortune which had dogged the Arcadian enterprise from the beginning, seemed to be gathering its forces for a final blow.

"Cloud-bursts?" he questioned. "Are they frequent in the head basin of the Boiling Water?"

"Not frequent, but very terrible when they do occur. I have seen the Elbow toss its spray to the top of this cliff—once, when I was quite small; and on that day the lower part of our valley was, for a few hours, a vast flood lake."

"Was that before or after the opening of your father's mine over yonder?" queried Ballard.

"It was after. I suppose the mine was flooded, and I remember there was no work done in it for a long time. When it was reopened, a few years ago, father had that immense bulkhead and heavy, water-tight door put in to guard against another possible flood."

Ballard made the sign of comprehension. Here was one of the mysteries very naturally accounted for. The bulkhead and iron-bound door of the zirconium mine were, indeed, fortifications; but the enemy to be repulsed was nature—not man.

"And the electric signal service system in the upper canyon is a part of the defence for the mine?" he predicated.

"Yes. It has served on two or three occasions to give timely warning so that the miners could come up and seal the door in the bulkhead. But it has been a long time since a cloud-burst flood has risen high enough in the Elbow to threaten the mine."

Silence supervened; the silence of the flooding moonlight, the stark hills and the gently lapping waters. Ballard's brain was busy with the newly developed responsibilities. There was a little space for action, but what could be done? In all probability the newly completed dam was about to be subjected to the supreme test, violently and suddenly applied. The alternative was to open the spillway gate, using the cut-off tunnel as a sort of safety-valve when the coming flood water should reach the Elbow.

But there were an objection and an obstacle. Now that he knew the condition of the honeycombed tunnel, Ballard hesitated to make it the raceway for the tremendously augmented torrent. And for the obstacle there was a mechanical difficulty: with the weight of the deepening lake upon it, the stop-gate could be raised only by the power-screws; and the fires were out in the engine that must furnish the power.

The Kentuckian was afoot and alert when he said: "You know the probabilities better than any of us: how much time have we before these flood tides will come down?"

She had risen to stand with him, steadying herself by the hook of the derrick-fall. "I don't know," she began; and at that instant a great slice of the zirconium mine dump slid off and settled into the eddying depths with a splash.

"It is nothing but a few more cubic yards of the waste," he said, when she started and caught her breath with a little gasp.

"Not that—but the door!" she faltered, pointing across the chasm. "It was shut when we came out here—I am positive!"

The heavy, iron-studded door in the bulkhead was open now, at all events, as they could both plainly see; and presently she went on in a frightened whisper: "Look! there is something moving—this side of the door—among the loose timbers!"

The moving object defined itself clearly in the next half-minute; for the two at the derrick-heel, and for another—young Blacklock, who was crouching behind his rejected thorough-stone directly opposite the mine entrance. It took shape as the figure of a man, slouch-hatted and muffled in a long coat, creeping on hands and knees toward the farther dam-head; creeping by inches and dragging what appeared to be a six-foot length of iron pipe. The king's daughter spoke again, and this time her whisper was full of sharp agony.

"Breckenridge! it is my father—just as I have seen him before! That thing he is dragging after him: isn't it a—merciful Heaven! he is going to blow up the dam! Oh, for pity's sake can't you think of some way to stop him?"

There are crises when the mind, acting like a piece of automatic machinery, flies from suggestion to conclusion with such facile rapidity that all the intermediate steps are slurred and effaced. Ballard marked the inching advance, realised its object and saw that he would not have time to intervene by crossing the dam, all in the same instant. Another click of the mental mechanism and the alternative suggested itself, was grasped, weighed, accepted and transmuted into action.

It was a gymnast's trick, neatly done. The looped-up derrick-fall was a double wire cable, running through a heavy iron sheave which carried the hook and grappling chains. Released from its rope lashings at the mast-heel, it would swing out and across the canyon like a monster pendulum. Ballard forgot his bandaged arm when he laid hold of the sheave-hook and slashed at the yarn seizings with his pocket-knife; was still oblivious to it when the released pendulum surged free and swept him out over the chasm.