The Birmingham reservoirs are a chain of lakes artificially produced by damming up the River Elan, a tributary of the Wye. The great aqueduct which carries the water from the Elan, eighty miles across country, travelling through hills and bridging valleys, runs past Ludlow and Cleobury Mortimer, through the Wyre Forest to Kidderminster, and on to Birmingham itself through Frankley, where there is a large storage reservoir from which the water is distributed.

The scenery was bleak and desolate. Before us the sun was sinking in a flood of crimson light. We walked briskly, the long legs of the Russian carrying him swiftly over the uneven ground while I trotted beside him. Before the last rays of the sun had died away we saw the black outline of the Caban Loch dam before us, and caught the sheen of water beyond. On the north lay the river Elan and on the south the steep side of a mountain towered up against the luminous sky. The road runs along the left bank of the river bounded by a series of bold and abrupt crags that rise to a height of some eight hundred feet above the level of the water. Just below the Caban Dam is a house occupied by an inspector in charge of the gauge apparatus that is used to measure the outflow of water from the huge natural reservoirs. The lights from his house twinkled through the growing darkness as we drew near, and we skirted it by a short detour and pressed on.

"How long does water take to get from here to Birmingham?" asked Sarakoff as we climbed up to the edge of the first lake.

"It travels about a couple of miles an hour," I replied. "So that means about a day and a half."

We spoke in low voices, for we were afraid of detection. The presence of two visitors at that hour might well have attracted attention.

"A day and a half! Then the bacillus has a long journey to take." He stopped at the margin of the water and stared across the shadowy lake. "Yes, it has a long journey to take, for it will go round the whole world."

The last glow in the sky tinted the calm sheet of water a deep blood colour. Sarakoff opened his bag and took out a couple of tubes.

He pulled the cotton-wool plugs out of the tubes, and with a long wire, loosened the gelatinous contents. Then, inverting the tubes he flung them into the lake close to the beginning of the huge aqueduct.

I stared as the tubes vanished from sight, feeling that it was too late to regret what had now been done, for nothing could collect those millions of bacilli, that had been set free in the water. Already some of them had perhaps entered the dark cavernous mouth of the first culvert to start on their slow journey to Birmingham. The light faded from the sky and darkness spread swiftly over the lake. Sarakoff emptied the remaining tubes calmly and then turned his footsteps in the direction of Rhayader. I waited a moment longer in the deep silence of that lonely spot; and then with a shiver followed my friend. The bacillus had been let loose on the world.