It was humid inside the small laboratory in spite of the window which was open contrary to all regulations. Outside the sun shone and, but for the absence of foliage on the trees surrounding the squat grey stone buildings which comprised the Midlands Biological Research Centre, one would have been forgiven for assuming that summer had already begun. Small birds twittered incessantly as they busied themselves searching for twigs and dry grass with .which to complete the building of their nests. Rooks circled and cawed noisily above a line of tall elms. Another cycle of life had begun.

The tall, fair-haired man in the long white coat moved away from the window and, ignoring the 'no smoking' sign above the long table which supported several oblong glass cases, he lit a cigarette, inhaled deeply, and slowly blew twin streams of smoke out through his nostrils. His handsome, tanned features wore a worried expression, his lips were a tight, bloodless line, his pale blue eyes focused on the end container. He drew even more fiercely on his cigarette, seemingly unaware of the attractive blonde girl who watched his every move intently.

The rats, mice and guinea pigs in the other cages were unnaturally still, almost as though they sensed that something untoward was happening in that very room, something totally in contrast to the laws of Nature, something which they could not understand but feared all the more because it was beyond their comprehension.

Even the reinforced glass could not muffle the shrill, almost insane shrieking of the bats within the cage. Usually they were motionless and silent by day, only becoming active when the laboratory was in darkness and the bacteriologists had left. Not so today. For the last three days they had been abnormally active, with the exception of those that lay dead on the floor of their prison. Even in death they had an unnatural look about them, the corpses stiff and twisted beyond the limits of rigor mortis, the tiny faces masks of pain and rage, proof that the creatures had died in extreme agony.