ashallow valley, along the bottom of which a rippling burn wound its way.Descending the hill they crossed the brook and soon found themselves ata tiny bridge beside the only gateway they could see in the high stonewall, surmounted by a formidable barrier of barbed iron, whichsurrounded the building.

  In response to Renstoke's knock the door was opened by an ill-favouredindividual, evidently a foreigner, who stared at them in blank surprise.

  "I want to see Mr Erckmann; is he at home?" Renstoke demanded.

  The man made some reply in a language which neither of them understood.Renstoke repeated his question.

  Turning to a telephone which stood on a small table in the lodge the manspoke a few words. A moment later he signed to them to enter andconducted them to the entrance door of the big house.

  As they approached a big, powerfully built man, heavily bearded andwearing round horn spectacles, met them on the steps of the front door.

  Renstoke bowed courteously. "Mr Erckmann?" he inquired.

  "Yes, I am Mr Erckmann," was the reply. "What can I do for you?"

  Renstoke as briefly as possible explained what had happened. Erckmannlistened patiently and carefully. Only at the end of the story, whenRenstoke told him quite frankly his suspicions, the man's eyes hardenedominously and his lips tightened under his heavy grey moustache.

  "Yes, I have a gorilla," he admitted. "But if you suggest that it hasescaped you are quite wrong. It has never left its cage since it wasbrought here, quite young, six years ago. It would be a bad thing forsome one if it did," he added.

  "May we see it?" asked Renstoke quietly.

  "Yes--if you doubt my word," snapped the scientist. He was evidently,for some reason, much annoyed and was controlling himself with obviousdifficulty.

  During the conversation Dick had once or twice glanced at Yvette and wassurprised at the fixity of the gaze she directed at Erckmann. She wasregarding him almost as if fascinated, with every sign of horror andapprehension.

  Without further words Erckmann led the way through a small paddock to arow of cages, heavily barred with iron, which stood at the rear of thehouse. Before one of the strongest he halted.

  "There you are," he said grimly.

  Inside the cage, erect on its hind legs, stood an enormous ape, shackledby a huge chain round its neck to a heavy stake driven into the ground.Nearly seven feet high, it was so horribly repulsive in its pervertedlikeness to humanity, that Yvette, Dick, and Jules turned away sick withdisgust and horror. It snarled and chattered at the sight of thestrangers.

  Renstoke, however, carefully examined the monster. But he soon realisedthat this creature had certainly not been at large, at any rate for someconsiderable time.

  The clue had failed. Whatever the truth might be it was clear thegorilla could have had no part in the terrible tragedy of AlanMacPherson.

  "A wonderful specimen," said Renstoke, turning to Erckmann. "Have youhad him long?"

  "About six years," the scientist replied. "Would you like to see whatit can do?" Without waiting for a reply, he spoke softly to the ragingbeast in some language the others did not understand.

  Instantly the brute calmed down, shuffled to the bars of the cage andlaid its head on the ground close to where Erckmann was standing. Itwas just as though a dog were fawning on its master. Erckmannfearlessly thrust a hand between the bars and scratched the repulsivehead while the great ape lay with closed eyes evidently in keenenjoyment of the sensation.

  Still talking quietly in the strange language, Erckmann put the beastthrough a number of tricks which it performed, clumsily, of course, butwith obvious understanding of what was required of it. It was, asRenstoke realised, a wonderful example of animal training, for thegorilla is perhaps the most intractable of all living animals.

  "Perhaps as you are here you would like to see the rest of mymenagerie," said Erckmann, as he led the way to a series of cagesadjoining.

  They gazed in astonishment at what they saw. There was a superb tiger,several leopards of different species, and at least a dozen wolves. Theanimals were all clean and well cared for and it was obvious at a glancethat none of them could have been wandering for an indefinite periodabout the country.

  "I hope you are satisfied, Lord Renstoke," said Erckmann at last, "thatnone of my pets is responsible for what has happened?"

  "Quite," replied Renstoke. "And I am sorry we had to trouble you. ButI am sure you will understand why I came. The affair is so mysteriousthat I could not leave any possibility unexplored." Erckmann hadpuzzled them all. The man was perfectly courteous and apparently quiteopen in his replies to their questions. None the less all sensed thathe was ill at ease and that he quite certainly resented their intrusion.

  Yvette, more sensitive and keenly strung than the others, shudderedviolently as they left the house.

  "That man is bad, all bad," she declared vehemently. "He has the eyesof the snake." She had put into words what all had felt, yet had beenhalf ashamed to confess. There was something repulsively snake-like inthe steady glare of Erckmann's eyes behind the thick round glasses.

  "I confess I feel like Yvette," said Dick, "the man gave me the creeps."

  Renstoke looked grave.

  "He didn't strike me as being quite aboveboard," he admitted. "At thesame time, I don't see what he has to conceal. All the cages wereoccupied and it is certain none of the animals had been loose recently,and if one had broken out there is no reason why he should not say so.But he may have another ape which he has not shown us?"

  They walked a few hundred yards in silence until they had got to thebottom of the hill and approached the little burn that ran down thevalley. There was no path, and as chance would have it, they deviated afew yards from the way along which they had come. They were crossingthe brook when Yvette gave a slight exclamation.

  "Oh, look here," she said.

  The bed of the burn was stony throughout, but at one point, at the veryedge of the water was a tiny patch of sand, smooth and firm and hardlylarger than a handkerchief. Yvette pointed to it.

  There, sharply and clearly defined, was the unmistakable imprint of anaked, misshapen foot! It was human beyond all question. It pointed inthe direction of the house they had just left, and it was dear that thebarefooted walker, whoever he may have been, had stepped from theheather just on to the patch of firm sand and been carried by his nextstride through and beyond the rivulet on to the heather and stones whereno footprints would remain. By some strange chance that one tell-talefootprint had been left in perhaps the only square foot of ground formiles where an impression could be left!

  They examined the footprint with eager curiosity. Evidently the walker,or rather runner, had come fast down the hill, for the front part of thefoot was driven deeply into the sand while the heel was only justshowing.

  "He must have been running," said Renstoke, "and what kind of man couldrun over such a country as this?"

  The question was natural, for the heather grew thick and deep roundthere and they had found walking difficult enough; running would havebeen out of the question for any of them.

  They were puzzled by the strange footprint, but how little they guessedthat it held the key to the terrible tragedy of Renstoke!

  Late that night, Renstoke, Dick, and Jules sat yarning in the great olddrawing-room at the Castle. The night was close and sultry, with athreat of thunder in the air, and the big French windows which opened onto the spreading lawn were flung wide.

  They were discussing Erckmann.

  "I didn't like him," said Renstoke, "though it is recognised that hepossesses genius in a marked degree."

  "Oh! You've heard something then?" asked Dick quickly.

  "Yes. The general public know nothing of him, but I hear that he has anamazing theory that it is possible, by an operation on the brain, toabolish almost entirely the ordinary characteristics of a man or ananimal, and by the injection of an appropriate serum to substitute themental, and to some extent the physical, c
haracteristics of anotherspecies. He believes that you can, for instance, take a puppy-dog,operate on its brain, inject a serum prepared in some way from the brainof a monkey, and the puppy will grow up with the mentality and habits ofa monkey and with its bodily characteristics so transformed that it cando many things--such, for instance, as climb a tree--which no dog coulddo. I believe he has actually succeeded in doing this!"

  "How weird and extraordinary!" remarked Yvette.

  "More than this, he believes you could do the same with a human being--destroy its human attributes and give it, for example, the ferocity, andsomething of the speed, of a wolf or a tiger."

  "How on earth did you learn this, Renstoke?" asked Dick.

  "From perhaps the only person who ever knew Erckmann really well," wasthe reply.