Martin Conisby's Vengeance by Jeffery Farnol

I waked to a scream, a fierce trampling, an awful snarling, this drowned in the roar of a gun, and started up to see a glitter of darting steel that Sir Richard sought to parry with his smoking weapon. Then I was up, and, sword in hand, leapt towards his assailant, a tall, bearded man whose corselet flashed red in the fire-glow and who turned to meet my onset, shouting fiercely. And so we fell to it point and point; pushing desperately at each other in the half-light and raving pandemonium about us until more by good fortune than skill I ran him in the arm and shoulder, whereupon, gasping out hoarse maledictions, he incontinent made off into the dark. Then turned I to find myself alone; even the Indian had vanished, though from the darkness near at hand was a sound of fierce strife and a ringing shot. Catching up a musket I turned thitherward, but scarce had I gone a step than into the light of the fire limped Sir Richard and Pluto beside him, who licked and licked at his great muzzle as he came.

"Oh, Martin! " gasped Sir Richard, leaning on his musket and bowing his head, "oh, Martin -- but for Pluto here -- " And now, as he paused, I saw the dog's fangs and tongue horribly discoloured.