Neither Brian nor Colter waited to receive the congratulations of their friends; they were speeding down the course to where a crowd had gathered about Greenpol, and a smaller crowd about the prostrate jockey.

They pushed their way through to find the lad shaken but unhurt, and then made their way to the horse.

He lay, his head stretched out, dead.

The doctor, who had followed them, joined them after he had seen the boy.

"I can't understand it," Colter was saying.

Ernest stooped and looked at the horse's muzzle. Something he had seen interested him. He ran his hand carefully along the neck of the dead animal.

"I thought so," he said. "I have seen horses die like this before, but not in this country."

"Where?"

"On the East Coast of Africa," the doctor replied. He had been a naval surgeon before an unexpected windfall had enabled him to purchase a practice in London.

"What do you think it is?" demanded Brian.

The doctor looked thoughtful.

"I would rather not say for a moment — it sounds palpably absurd. Let us get back to the stands."

They walked back together, after giving instructions for the disposal of the dead horse.

"One theory I will give you," said Ernest, "and that is, that an attempt was made to get at Grey Timothy and the horse that shared his stable suffered. I want you to keep Timothy away from Colter's place for a day or so."

"Certainly," agreed Brian.

"And I think it would be wise if we went straight back to the stables — I want to make a little investigation."

Neither Mr Callander nor his daughter offered any objection. The old man was immensely elated, very voluble — for him — and thoroughly reconciled to the Turf. Brian remembered with an inward smile that Mr Callander had backed the winner.

The girl met Brian on the lawn of the enclosure.

"Is that poor horse dead?" she asked with deep concern in her voice.

"Yes, I'm afraid he is," said Brian quietly, "and I am going to find out why he died."

She asked no further question. She knew instinctively something had happened which overshadowed the satisfaction of Grey Timothy's victory.

They stayed long enough to interview the grey in his box. He showed no sign of the struggle he had made. Sheeted and wrapped from neck to tail, he turned his inquiring eyes upon his visitors, and gave no indication of elation, till Colter came up to him to fondle his neck. Then Grey Timothy unbent to the extent of switching his tail twice, usually a sign of temper, but, in his case, a sedate method of greeting.

Their swift car carried them back to the trainer's establishment, and when the party had been disposed of and went to tea and rest after their exciting day, the three men — Brian, the trainer, and Ernest — made their way to the box which had held Timothy and his ill-fated companion.

Before they examined the interior, the doctor beckoned a stable lad.

"Have you a birch broom?" he asked, and the man brought him one.

"Do you mind my damaging your property?" asked Ernest.

"Go ahead," said Colter.

With a knife the doctor cut the band which fastened the long twigs to the broom handle. He selected twenty or thirty of the longest and tied them together in the form of a familiar instrument of punishment.

Armed with this he stepped into the stable, and began a careful search. At his request, the others remained in the doorway looking on in wonder. They saw him scrutinizing the place, inch by inch. First the clean-tiled floor of the box, then the walls.

For a time nothing happened, then he raised his switch swiftly and brought it down upon the wall. He took a match-box from his pocket, emptied the contents on the floor, stooped and picked up something and placed it in the empty box. Then he resumed his search, and the onlookers noticed that he was confining himself to the side of the stable in which Greenpol had been housed.

Swish!

Down came the switch again, and again he stooped to pick up something and carefully place it in the receptacle he had provided.

After a while he called for a step-ladder and they brought it. Stealthily he climbed it, and aimed a blow at a rafter above his head.

He descended to place his prize with the others. Another quarter of an hour's search failed to reveal anything more, and he came out into the sunlight, resuming the coat he had abandoned in the midst of his quest.

"You had better have all the doors and windows and ventilators hermetically sealed," he said to Mr Colter; "then bum a pound or so of sulphur."

He took the box from his pocket and opened it.

There were three dead flies. They were jet black and a little bigger than the common housefly, and the wings, which were folded over the back, overlapped.

"You see," said Ernest, as he turned them over with a match, "their wings are crossed like scissor-blades."

"What are they?" asked Brian.

"Tsetse flies," said the doctor; "they are a native of South Africa, but more particularly of East Africa. Somebody has introduced them into your stables, and in some mysterious manner they have missed Timothy. Have you got a veterinary hand-book?"

"I have one in my study," said Colter, and to the study they adjourned. The trainer produced the book and Ernest opened it at the tropical section.

"Here you are," he said, and read:

"'The tsetse fly is the curse of East Africa. His sting is fatal to ox, horse or dog. Dr Koch, in his investigations, discovered that a semi-immunity from the bite of this insect is enjoyed by grey horses, the flies for some reason avoiding horses of this colour if other horses, less protected by Nature, are available'. That explains it," said the doctor.

"But it doesn't explain how they came here," said Brian grimly. "And when I find the brute that did such a devilish thing he'll be sorry."

A few moments later they rejoined the party.

"Your tea is quite undrinkable," smiled the girl.

"Finding more winners?" asked Mr Callander waggishly.

Only Horace, who for some reason had been rendered uncomfortable by the absence of the men, said nothing.

"No," said Brian, "but I've found something as interesting — I'm going to take all you good people into my confidence."

And in as few words as possible he told them of what had happened.

"What a dreadful thing!" gasped the girl. "Oh, how cruel!"

Mr Callander was red with wrath.

"Monstrous!" he stormed. "It is the most villainous thing I have ever heard of."

"But how could the flies have reached the stable?" asked the girl; "how — why, H — what is the matter?"

Horace was white to the lips, he swayed backward and forward, and appeared as if he were going to faint.

"Nothing," he said hoarsely; "the room is rather close, that is all."

The diversion turned the conversation. Greatly distressed by his favourite's sudden illness, Mr Callander assisted Brian to pilot him to the open air. He recovered after a while.

"Let us get home," he muttered. "I am tired of this business."

"Yes, yes, my dear," soothed his father. "We'll go as soon as you like."

It was by no means to Brian's taste that the tête-á-tête he had promised to himself should be abandoned. He begged Mr Callander to stay, but where the wishes of his son were concerned the elder man was wax.

The car was got ready and in an incredibly short space of time they were watching it disappearing along the London road.

Brian had just time to exchange a word with the girl.

"I'm sorry we've got to leave so suddenly," she said, "and I'm so sorry about Greenpol, and so glad that Grey Timothy won."

"That is all right," he said; "the only thing I want to ask you is — will you marry me?"

She had said nothing. He had assisted her into the car and had exchanged conventional farewells with her, and she had heard them as in a dream. She was half-way to London before she began to wake from her trance into which his staggering proposal had stunned her.

Then as she realized the immensity of the occurrence she felt unaccountably annoyed. A woman is something of a ritualist in love-making. Then she laughed — it was so like Brian.

That individual watched the car until it was out of sight, then stood watching the little hill over the crest of which it had disappeared.

"What made young Callander so ill?" he asked the doctor; "has he got a weak heart?"

Ernest shook his head.

"I should think not — it looked to me like — "

He hesitated.

"Funk?" suggested Brian. "Well, to be frank, yes."

"Do you think he had anything to do with the matter?"

"I do — I was watching him absent-mindedly whilst you were talking to his father and sister. The news of the tsetse seemed to strike him all of a heap."

"I wonder if he knows. By Jove, Colter, he was here yesterday; don't you remember he was awfully confused about something? Oh, yes, his overcoat! He wanted to carry it. I'll take six to four the bugs were in the pocket of that coat!"

"It shouldn't be difficult to discover how they came," said Ernest. "The field of supply is a very limited one. I suppose there are only two places in England where live tsetses can be obtained the Liverpool and London Schools of Tropical Medicines. I will wire them asking if they can supply us with a dozen flies."

The wires were despatched, the answers came that night, and were almost identical:

"We cannot supply; suggest you apply Dr Jellis of Watford."