Presently,—­not relishing the rebukes of the friends who had heretofore pestered him by overmuch petting,—­the collie arose quietly from his couch of trampled earth at the foot of the stone bench and strolled back across the street.  Most of the men were too busy, talking, to note Bruce’s departure.  But Sergeant Mahan caught sight of him just as the dog was mounting the last of the steps leading into the church.

As a rule, when Bruce went investigating, he walked carelessly and with his tail slightly a-wag.  Now his tail was stiff as an icicle, and he moved warily, on the tips of his toes.  His tawny-maned neck was low.  Mahan, understanding dogs, did not like the collie’s demeanor.  Remembering that the nurse had entered the church a few minutes earlier, the Sergeant got to his feet and hastily followed Bruce.

The dog, meanwhile, had passed through the crazily splintered doorway and had paused on the threshold of the improvised hospital, as the reek of iodoform and of carbolic smote upon his sensitive nostrils.  In front of him was the stone-paved vestibule.  Beyond was the interior of the shattered church, lined now with double rows of cots.

Seated on a camp-chair in the shadowy vestibule was the pseudo Red Cross nurse.  At sight of the collie the nurse got up in some haste.  Bruce, still walking stiff-legged, drew closer.

Out from under the white skirt flashed a capable and solidly-shod foot.  In a swinging kick, the foot let drive at the oncoming dog.  Before Bruce could dodge or could so much as guess what was coming,—­the kick smote him with agonizing force, square on the shoulder.

To a spirited collie, a kick carries more than the mere pain of its inflicting.  It is a grossly unforgivable affront as well—­as many a tramp and thief have learned, at high cost.

By the time the kick had fairly landed, Bruce had recovered from his instant of incredulous surprise; and with lightning swiftness he hurled himself at his assailant.

No bark or growl heralded the murderous throatlunge.  It was all the more terrible for the noiselessness wherewith it was delivered.  The masquerading man saw it coming, just too late to guard against it.  He lurched backward, belatedly throwing both hands up to defend his throat.  It was the involuntary backward step which saved his jugular.  For his heel caught in the hem of his white skirt.  And wholly off balance, he pitched headlong to the floor.

This jerky shift of position, on the part of the foe, spoiled Bruce’s aim.  His fearful jaws snapped together harmlessly in empty air at a spot where, a fraction of a second earlier, the other’s throat had been.  Down crashed the disguised man.  And atop of him the furious dog hurled himself, seeking a second time the throatgrip he had so narrowly missed.

At this point on the program Sergeant Mahan arrived just in time to bury both hands in the mass of Bruce’s furry ruff and to drag the snarlingly rabid dog back from his prey.