He saw Mortimer FitzHugh with a revolver in his hand.

He had stopped; he was staring like one looking upon the ghost of the dead, and as he stared there rose above the rumbling roar of the chasm a wild and terrible shriek from Joanne.
Aldous saw no more then.

He was not fighting for his life, but for her, and he fought with the mad ferocity of a tiger.

As he struck, and choked, and beat the head of his assailant on the rock, he heard shriek after shriek come from Joanne's lips; and then for a flash he saw them again, and Joanne was struggling in the arms of Quade! He struggled to his knees, and the man he was fighting struggled to his knees; and then they came to their feet, locked in a death-grip on the edge of the chasm.

From Quade's clutch he saw Joanne staring at Mortimer FitzHugh; then her eyes shot to him, and with another shriek she fought to free herself.
For thirty seconds of that terrible drama Mortimer FitzHugh stood as if hewn out of rock.