Stanford Beale spent a thoughtful three minutes in the darkness of the cellar passage to which Hilda Glaum had led him and then he began a careful search of his pockets. He carried a little silver cigar-lighter, which had fortunately been charged with petrol that afternoon, and this afforded him a beam of adequate means to take note of his surroundings.

The space between the two locked doors was ten feet, the width of the passage three, the height about seven feet. The roof, as he had already noted, was vaulted. Now he saw that along the centre ran a strip of beading. There had evidently been an electric light installation here, probably before the new owners took possession, for at intervals was a socket for an electric bulb. The new occupants had covered these and the rest of the wall with whitewash, and yet the beading and the electric fittings looked comparatively new. One wall, that on his left as he had come in, revealed nothing under his close inspection, but on the right wall, midway between the two doors, there had been a notice painted in white letters on a black background, and this showed faintly through the thick coating of distemper which had been applied. He damped a handkerchief with his tongue and rubbed away some of the whitewash where the letters were least legible and read:

AID
LTER.
------
ULANCE &
T AID.

This was evidently half an inscription which had been cut off exactly in the middle. To the left there was no sign of lettering. He puzzled the letters for a few moments before he came to an understanding.

"Air-raid shelter. Ambulance and first aid!" he read.

So that explained the new electric fittings. It was one of those underground cellars which had been ferreted out by the Municipality or the Government for the shelter of the people in the neighbourhood during air-raids in the Great War. Evidently there was extensive accommodation here, since this was also an ambulance post. Faintly discernible beneath the letters was a painted white hand which pointed downward. What had happened to the other half of the inscription? Obviously it had been painted on the door leading into the first-aid room and as obviously that door had been removed and had been bricked up. In the light of this discovery he made a more careful inspection of the wall to the left. For the space of four feet the brickwork was new. He tapped it. It sounded hollow. Pressing his back against the opposite wall to give him leverage he put his foot against the new brickwork and pushed.

He knew that the class of workmanship which was put into this kind of job was not of the best, that only one layer of brick was applied, and it was a mechanical fact that pressure applied to the centre of new work would produce a collapse.

At the first push he felt the wall sag. Releasing his pressure it came back. This time he put both feet against the wall and bracing his shoulders he put every ounce of strength in his body into a mighty heave. The next second he was lying on his back. The greater part of the wall had collapsed. He was curious enough to examine the work he had demolished. It had evidently been done by amateurs, and the whitewash which had been thickly applied to the passage was explained.

A current of fresh air came to meet him as he stepped gingerly across the debris. A flight of six stone steps led down to a small room containing a sink and a water supply, two camp beds which had evidently been part of the ambulance equipment and which the new owners had not thought necessary to remove, and a broken chair. The room was still littered with the paraphernalia of first-aid. He found odd ends of bandages, empty medicine bottles and a broken glass measure on the shelf above the sink.

What interested him more was a door which he had not dared to hope he would find. It was bolted on his side, and when he had slid this back he discovered to his relief that it was not locked. He opened it carefully, first extinguishing his light. Beyond the door was darkness and he snapped back the light again. The room led to another, likewise empty. There were a number of shelves, a few old wine-bins, a score of empty bottles, but nothing else. At the far corner was yet another door, also bolted on the inside. Evidently van Heerden did not intend this part of the vault to be used.

He looked at the lock and found it was broken. He must be approaching the main workroom in this new factory, and it was necessary to proceed with caution. He took out his revolver, spun the cylinder and thrust it under his waistcoat, the butt ready to his hand. The drawing of the bolts was a long business. He could not afford to risk detection at this hour, and could only move them by a fraction of an inch at a time. Presently his work was done and he pulled the door cautiously.

Instantly there appeared between door and jamb a bright green line of light. He dare not move it any farther, for he heard now the shuffle of feet, and occasionally the sound of hollow voices, muffled and indistinguishable. In that light the opening of the door would be seen, perhaps by a dozen pair of eyes. For all he knew every man in that room might be facing his way. He had expected to hear the noise of machinery, but beyond the strangled voices, occasionally the click of glass against glass and the shuff-shuff-shuff of slippered feet crossing the floor, he heard nothing.

He pulled the door another quarter of an inch and glued his eye to the crack. At this angle he could only see one of the walls of the big vault and the end of a long vapour-lamp which stood in one of the cornices and which supplied the gha............