There was another tricky point to the system. The lead car of The Shadow's pursuit party should logically have followed the tail car of Zune's caravan, since it was the easiest to overtake. That was the way The Shadow's agents had tried it, the night they had made a chase from Stanwich. But on this occasion, the first pursuing car took the route that the leader of the fleeing caravan had used.

Margo and Gail saw the result. Having taken the shortest course in this blind game, The Shadow's car, first of the pursuit party, was gaining its objective at the expense of the last car in Zune's group. Just at the last car made that fancy veer, The Shadow's car sighted it.

There was time for Zune's last car to scoot from sight; time, too, for the concrete portal to slide shut. But The Shadow had cracked the system. His car duplicated that wide swing over toward the b.u.t.tress; the barrier opened and The Shadow stayed on the trail.

So did the rest of The Shadow's cars. Coming by the various routes, in the same order the Zune's cars had used, the pursuers saw exactly what awaited them and copied The Shadow's system to the dot.

Gail drew a long breath and said: "Just try to imagine that!"

"I can't," rejoined Margo. "Not even after seeing it happen!"

"Well, we did see it happen," Gail declared, "and there's nothing to stop us from trying it ourselves."

Try it they did when they reached the clover-leaf and when the concrete opened magically in front of them, the girls found their car burrowing right through a tunnel beneath the superhighway.

Something struck home to Gail.

"This was one of those contracts let out by Sark!" Gail exclaimed. "We never could understand what happened to some of the materials. We were sure they were delivered, because the highway was completed, but it seemed just tons and tons short of concrete!"

"It came from here then," returned Margo, "or rather this is where it didn't go. I have an idea where it is though."

"So have I," declared Gail with a nod. "Bolstering that underground citadel that Sark built for Zune to occupy!"

"Somehow Sark strikes me as the real genius," mused Margo aloud, "and therefore the more dangerous. This highway would have been good for ten years before it began to cave and by then its purpose would be served."

"There must be a dozen others like it," said Gail, unhappily, "all places where that White Skull crowd could vanish and disappear. My father had all these contracts and Sark figured in every job."

Coming out thorough a camouflaged exit that lifted like a portcullis, the car swung into a narrow by-road that Gail recognized as one leading toHartfield. The tunnel had carried them off through a hill, away from the superhighway. Then Gail remembered something else.

"There's another of those clover-leafs near Hartfield," Gail told Margo.

"I.

suppose we'll find the same thing there. If we do, I can guess where it will lead."

"Under the old museum?"

"Either that or pretty close to it."

"If we do," decided Margo, "we'd better drive into the tunnel. There's nothing we can do to hurt and there might be some way we could help."

There was good reason for the confidence in Margo's tone. She felt sure that The Shadow's plans - like those of others - were coming to a climax.

When that happened, bets were best laid on The Shadow.

CHAPTER XX.

WHIPPING into the outskirts of Hartfield, a speedy coupe took the hill leading up to the Crabtree Museum. Coming around a final turn, the car gave quick toots of its horn and a big gate swung open.

Next the coupe rolled into an inside court where men were loading quant.i.ties of crates and bulky frames into some waiting trucks. The coupe stopped and Jud Mayhew stepped from one door; Philo Brenz from the other.

Promptly, Brenz convinced the truckers that he had a right to be here. He was ushered into the museum itself to find some attendants helping pack the art treasures. The hired help at the museum had been expecting the trucks almost any day and were glad that they had arrived so soon.

So was Jud Mayhew.

Jud's only wish was that the truckers might have arrived sooner. Still, there was time for them to get everything out before Tanjor Zune arrived. At least Brenz thought so, for he stepped right into the position of supervisor and began to make things move.

Apparently taking it for granted that the more important treasures had been stored away from public eye, Brenz asked where the vaults were and was shown there. Jud went along and the truck men followed, down to a great arched cellar where goods were already packed.

Hardly had the truckers and attendants started to remove the ma.s.sive crates from the cellar before the dreaded stroke arrived. The whole building seemed to quiver as it absorbed the vibrations of a peculiar explosion that had a flowing effect, as though spreading itself up through the foundations of the museum.

The floor heaved itself apart as men recoiled from its upward thrust.

Then, from what seemed a self-splitting mole hill of gigantic size, invaders appeared, wearing the black costumes that bore the painted skeleton ribs and hooded death's heads of the White Skull.

The truck men must have sensed such danger while it was still on the way.

As they fell back to the corners of the great cellar, they drew revolvers to offset the guns that the invaders displayed. Philo Brenz did the same; stepping forward, gun in hand, he was about to call for combat when Tanjor Zune appearedfrom the slanted gap in the cellar floor.

Zune barked an order and his men spread to vantage spots. Gun for gun, Zune faced Brenz while the truck men, Jud among them, dodged for shelter of their own. Both groups seemed to cancel themselves in pairs, leaving the field to Brenz and Zune.

The thing became an immediate stalemate. All around the cellar were pillars, supporting its vaulted roof. Those pillars served as the shelter that both fractions needed. Each group seemed dubious about starting battle, fearing to heap reprisal on itself.

And Jud, finding himself an ex-officio member of the trucking crew, decided that he'd better stay right where he was, until something broke this spell.

Face to face, Zune and Brenz were eyeing each other like creatures from another world. Then Zune spoke, in that harsh, fierce tone of his.

"I should have known you would be here," declared Zune. "Whoever you are, whatever your name, you had too much at stake to stay away."

"The mistake was yours," retorted Brenz, abruptly. "You were a fool not to know when you had lost - as I did."

Staring, Jud could hardly believe what he heard.

"I have not lost," sneered Zune. "I am proceeding with a duty. I am here to take the treasures."

"Which proves you are a fool," specified Brenz. "The thing at Stanwich is still a mystery, but if the contents of this museum are stolen, it will be no riddle."

Zune eyed Brenz sharply. Then: "Speaking of riddles," queried Zune, "why are you here to steal the treasures?"

"Only because you are," was Brenz's cool reply. "When I learned you were on the way, I had no other choice."

"You forget one thing." Zune's tone was rising, angrily. "I was the man appointed to take all this in charge!"

"I had more than an appointment," stormed Brenz. "I was promised full control once the work was done!"

Zune's anger suddenly changed to contempt.

"Everywhere there must be a leader," he declared proudly. "But to be successful in a country not yet conquered, that leader must depend upon some person there. A person who, to the world, is called a traitor - such as you."

"The greatest traitor," retorted Brenz, "is the man who hires one."

Knowing that the epithet was meant for him, Zune snarled back a single word that applied to Brenz.

That word, singularly suited to the term of perfidy, carried a contemptuous sound. The name that Zune had for Brenz was: "Quisling!"

That utterance cleared Jud's brain.

It meant just this and simply. Zune was the leader of a criminal band, come to America and stranded here, no longer able to serve the purposes of the defunct n.a.z.i regime. But to prepare for his arrival, Zune had needed the services of a man ready to betray his own country.

Such a man was Philo Brenz.

Brenz had been approached; he had done more than listen. It was Brenz who had supplied the ways and means of underbidding his own contracts and attributing the crooked work to Townsend North. Of all persons, Brenz was bestequipped to stage such underhanded action, while North was equally eligible as his dupe.

But there was one man who had arranged both angles, a man who was the perfect go-between: Alban Sark.

Jud's mere thought of the name produced the man in question.

As Zune and Brenz stood glaring at each other, a harsh laugh intervened.

There, emerged from the hole that Zune had hewn with Formula Four Hundred, stood Sark. How he had come along with Zune's own crew was a slight mystery in itself.

For the present, the important thing was the fact that Alban Sark had arrived.

The grin from Sark's skullish face was more livid than ever. He seemed to relish this scene.

"Allow me to introduce you," spoke Sark. "Tanjor Zune, leader of the White Skulls, intended as the shock troops of an occupation force. Philo Brenz, the man appointed to be America's Quisling. Both disappointments to themselves - as well as to each other."

For the first time, Zune and Brenz found themselves in agreement. That agreement was their hostility toward Sark.

"I am no disappointment," argued Zune. "I am here to take wealth as my own, that is all!"

"I have been trying to keep what I gained," declared Brenz. "I landed plenty of contracts and high priced ones. Why should I sacrifice my profits for a t.i.tle that no longer counts, or for treasures I could not keep?

Zune wheeled toward Brenz.

"You were after the treasures here -"

"To keep them from you," interrupted Brenz, "as I told you. I hoped to get them safely away and let you take the blame for a raid that failed. Perhaps they would never have found you, Zune, but they never would have even suspected me."

Zune's only answer was a glare. It was Sark who spoke and mockingly.

"Brenz is right, Zune," argued Sark. "You failed to learn who the Quisling was -"

"Because you never told me," interposed Zune, fiercely. "You said it was your business - not mine. Now I know why!"

"And why?"

"Because you made a deal with Brenz. You were to share his profits. Am I right?"

"Quite right." It was Brenz who gave the answer. "I made a deal with Sark.

I was too clever to try to kill him, even if I had wanted."

That thrust deflated Zune. Brusquely, he tried to throw it off. With a wave toward the men who waited behind pillars on Brenz's side of the cellar, Zune demanded: "These men? Who are they?"

Sark eyed the faces that were half-poked in sight and answered: "Brenz's servants. I have seen them before."

Brenz nodded that Sark was right. More than once, Sark had been a secret visitor to Brenz's apartment. Then: "I needed you again tonight, Sark," stated Brenz. "I tried to dispose of The Shadow, but it did not work. Remember that note you sent me once, saying tomeet you at Thorneau Place? I added a threatening paragraph at the front of it, on that old typewriter that used to be yours."

Sark gave a grinning smile, as though he appreciated the ruse even though it had failed. Then, Sark's drawn lips stiffened. He turned to Zune.

"I prefer men who do not fail," announced Sark. "Perhaps you have better claim to that, Zune. Of course" - Sark swung to Brenz - "I am open for conviction. Since all these treasures are at stake" - Sark was sweeping the well stocked cellar with his glistening gaze - "what is the use to wait?"

Cold words, but they raised the rivalry between Zune and Brenz to a white-hot pitch. Neither waited for the other; both wheeled and bellowed for the attack to begin. Like unleashed hound packs, Zune's fighters surged to meet Brenz's servants, who launched themselves with equal fury.

One man wasn't in that fray.

That man was Jud, who no longer belonged on Brenz's side and wouldn't fight on Zune's. As his target, Jud took a neutral who in Jud's estimate was the real menace in this case. All Jud wanted was to settle scores with Alban Sark, otherwise White Skull.

Sark's face seemed to loom gigantically as Jud drove forward, opening fire with his gun. Only it wasn't Sark at all, it was that old illusion, that of a white skull coming as an optical reflex after staring at a darkish face with grinning teeth and glistening eyes.

It seemed to float ahead of Jud, that thing that wasn't there, until Jud found himself actually tripping into the pit that represented the newly hewn tunnel. There, Jud was caught by a rising figure that emerged as suddenly as Sark had disappeared.

The Shadow!

A strident laugh sounded above the rattle of the gunfire with which Zune's men and Brenz's were chopping each other down. Reeling fighters turned to see The Shadow brushing Jud aside with a sweep of cloaked arms that brought two huge automatics into a pair of gloved fists.

From amid their faltering followers, Zune and Brenz wheeled apart, each intent upon being the first to deliver a concluding treatment to The Shadow.

Both were too late. The Shadow's shots came first. Flame-tonguing automatics drilled the rivals who had tried to salvage all they could from a ruined scheme, but who had each wanted all for his own and therefore had lost.

As they sprawled, Tanjor Zune and Philo Brenz looked up with glazing eyes and saw the face that was beneath The Shadow's slouch hat, which he had purposely tilted back.

It was the face of Alban Sark!

Jud Mayhew saw it too and couldn't believe it, until The Shadow cloaked a gun and used his hand to wipe that face away. On the floor he flung a gauze mask of that same molded pattern that he had given Jud for a temporary disguise. A tug of The Shadow's hat brim and his own face, that of Cranston, was obscured.

Zune's voice croaked from the floor.

"So we did blast Sark - that night in Stanwich -"

"But you couldn't believe your luck," coughed Brenz. "When Sark showed up again, you didn't guess he was The Shadow."