Thus nearly an hour wore on.  A fat moon butted its lazy way through the smoke-mists of the eastern skyline.

Then something happened—­something that Bruce could readily have forestalled if the wind had been blowing from the other direction, and if a dog’s eyes were not as nearsighted as his nose is farsmelling.

The Missourian paused to run his hand caressingly over the collie’s rough mane, and moved on, down the lonely beat.  Bruce watched his receding figure, drowsily.  At the end of ninety yards or more, the Missourian passed by a bunch of low bushes which grew at the near side of a stretch of hilly and shellpocked ground.  He moved past the bushes, still watched by the somewhat bored dog.

It was then that Bruce saw a patch of bushshadow detach itself from the rest, under the glow of the rising moon.  The shadow was humpy and squat.  Noiseless, it glided out from among the bushes, close at the sentry’s heels, and crept after him.

Bruce pricked his ears and started to get up.  His curiosity was roused.  The direction of the wind prevented him from smelling out the nature of the mystery.  It also kept his keen hearing from supplying any clue.  And the distance would not permit him to see with any distinctness.

Still his curiosity was very mild.  Surely, if danger threatened, the sentinel would realize it.  For by this time the Shadow was a bare three feet behind him near enough, by Bruce’s system of logic, for the Missourian to have smelled and heard the pursuer.  So Bruce got up, in the most leisurely fashion, preparatory to strolling across to investigate.  But at almost his first step he saw something that changed his gracefully slouching walk into a charging run.

The Shadow suddenly had merged with the sentinel.  For an instant, in stark silence, the two seemed to cling together.  Then the Shadow fled, and the lanky Missourian slumped to the earth in a sprawling heap, his throat cut.

The slayer had been a deft hand at the job.  No sound had escaped the Missourian, from the moment the stranglingly tight left arm had been thrown around his throat from behind until, a second later, he fell bleeding and lifeless.

In twenty leaping strides, Bruce came up to the slain sentinel and bent over him.  Dog-instinct told the collie his friend had been done to death.  And the dog’s power of scent told him it was a German who had done the killing.

For many months, Bruce had been familiar with the scent of German soldiers, so different from that of the army in which he toiled.  And he had learned to hate it, even as a dog hates the vague “crushed cucumber” smell of a pitviper.  But while every dog dreads the viper-smell as much as he loathes it, Bruce had no fear at all of the boche odor.  Instead, it always awoke in him a blood-lust, as fierce as any that had burned in his wolf-ancestors.

This same fury swept him now, as he stood, quivering, above the body of the kindly man who so lately had petted him; this and a craving to revenge the murder of his human friend.