Seemingly unaware of their great height, and the certain death the slightest misstep would bring, Doc swung around the group and back the easy route they had come. He pointed to a girder which, because of the roof effect of another girder above, was dry on one side. But there was a damp smear on the dry steel.

"The sniper rubbed it with his shoulder in passing," Doc explained. "That shows how tall he is. It also shows he has wide shoulders, because only a wide-shouldered man would rub the girder. Now — "

Doc fell suddenly silent. As rigid as if he were the bard bronze he so resembled, he poised against the girder. His glittering golden eyes seemed to grow luminous in the darkness.

"What is it, Doc?" asked Renny.

"Some one just struck a match — up there in the room where we were shot at!" He interrupted himself with an explosive sound. "There! He's lighted another!"

Doc instantly whipped the binoculars — he had brought them along from the office — from his pocket. He aimed them at the window.

He got but a fragmentary glimpse. The match was about burned out. Only the tips of the prowler's fingers were clearly lighted.

"His fingers — the ends are red!" Doc voiced what he had seen.

An interval of a dozen seconds, Doc waited.

"Let's go!" he breathed then. "You fellows make for that room, quick!"

The five men spun, began descending from the platform as swiftly as they dared. But it would take then minutes in the darkness, and the jumble of girders, to reach the spot where the elevators could carry them on.

"Where's Doc?" Monk rumbled when they were down a couple of stories.

Doc was not with them, they now noted.

"He stayed behind!" snapped waspish Ham. Then, as Monk accidentally nudged him in the dangerous murk: "Listen, Monk, do you want me to kick you off here?"

Doc, however, had not exactly remained behind. He had, with the uncanny nimbleness of a forest-dwelling monkey, flashed across a precarious path of girders, until he reached the supply elevators, erected by the workmen on the outside of the building for fetching up materials.

The cages were hundreds of feet below, on the ground, and there was no one to operate the controls. But Doc knew that. On the lip of the elevator shaft, balanced by the grip of his powerful knees, he shucked off his coat. He made it into a bundle in his hands.

The stout wire cables which lifted the elevator cab were barely discernible. A full eight feet out over space they hung. But with a gentle leap, Doc launched out and seized them. Using his coat to protect his palms from the friction heat sure to be generated, he let himself slide down the cables.

Air swished past his ears, plucked at his trouser legs and shirt sleeves. The coat smoked, began to leave a trail of sparks. Halfway down, Doc braked to a stop by tightening his powerful hands, and changed to a fresh spot in the coat.

So it was that Doc had reached the street even while thin, waspish Ham was threatening to kick the gigantic Monk off the girder if Monk shoved him again.

It was imperative to get to the office before the departure of the prowler who had lighted the match. Doc plunged into the taxi he had left standing in front, rapped an order.

Doc's voice had a magical quality of compelling sudden obedience to an order. With a squawl of clashing gears and a whine of spinning tires, the taxi doubled around in the street. It covered the several blocks in a fraction of a minute.

A bronze streak, Doc was out of the cab and in the skyscraper lobby. He confronted the elevator operator.

"What sort of a looking man did you take up to eighty-six a few minutes ago?"

"There ain't a soul come in this building since you left!" said the elevator operator positively.

Doc's brain fought the problem an instant. He had naturally supposed the sniper had invaded the room above. It seemed not.

"Get this!" he clipped at the operator. "You wait here and be ready to sic my five men on anybody who comes out of this building. My men will be here in a minute. I'm taking your cage up!"

In the cage with the last word, Doc sent it sighing upward a couple of city blocks. He stopped it one floor below the eighty-sixth, quitted it there, crept furtively up the stairs and to the suite of offices which had been his father's, but which was now Doc's own.

The suite door gaped ajar. Inside was sepia blackness that might hold anything.

Doc popped the corridor lights off as a matter of safety. He feared no encounter in the dark. He had trained his ears by a system of scientific sound exercises which was a part of the two hours of intensive physical and mental drill Doc gave himself daily. So powerful and sensitive had his hearing become that he could detect sounds absolutely inaudible to other people. And ears were all important in a scrimmage in the dark.

But a quick round of the three rooms, a moment of listening in each, convinced Doc the quarry had fled.

His men arrived in the corridor with a great deal of racket. Doc lighted the offices, and watched them come in. Monk was absent.

"Monk remained downstairs on guard," Renny explained. Doc nodded, his golden eyes flickering at the table. On that table, where none had been before, was propped a blood-red envelope!

Crossing over quickly, Doc picked up a book, opened it and used it like pincers to pick up the strange scarlet missive. He carried it into the laboratory, and dunked it in a bath of concentrated disinfectant fluid, stuff calculated to destroy every possible germ.

"I've heard of murderers leaving their victims an envelope full of the germs of some rare disease," he told the others dryly. "And remember, it was a strange malady that seized my father."

Carefully, he picked the crimson envelope apart until he had disclosed the missive it held. Words were lettered on scarlet paper with an odious black ink. They read:

SAVAGE: Turn back from your quest, lest the red death strike once again.

There was no signature.

A silent group, they went back to the room where they had found the vermilion missive.

IT was Long Tom who gave voice to a new discovery. He leveled a rather pale hand at the box which held the ultraviolet light apparatus.

"That isn't sitting where we left it!" he declared.

Doc nodded. He had already noticed that, but he did not say so. He made it a policy never to disillusion one of his men who thought he had been first to notice something or get an idea, although Doc himself might have discovered it far earlier. It was this modesty of Doc's which helped endear him to everybody he was associated with.

"The prowler who came in and left the red note used the black-light apparatus," he told Long Torn. "It's a safe guess that he inspected the window Johnny put together."

"Then he read the invisible writing on the glass!" Renny rumbled.

"Very likely."

"Could he make heads or tails of it?"

"I hope he could," Doc said dryly.

They all betrayed surprise at that, but Doc, turning away, indicated he wasn't ready to amplify on his strange statement. Doc borrowed the magnifying glass Johnny wore in his left spectacle, lens, and inspected the door for finger prints.

"We'll get whoever it was!" Ham decided. The waspish lawyer made a wry smile. "One look at Monk's ugly phiz and nobody would try to get out of here."

But at that instant the elevator doors rolled back, out in the corridor.

Monk waddled from the lift like a huge anthropoid.

"What d'you want?" he asked them.

They stared at him, puzzled.

Monk's big mouth crooked a gigantic scowl. "Didn't one of you phone downstairs for me to come right up?"

Doc shook his bronze head slowly. "No."