He lay staring at the rough stone wall close to his face, and it seemed to him that his future was bounded by a barrier as implacable and terrible as that.
"The Eye of Dread"
Payne Erskine
However implacable Stas in his soul was towards the Mahdists, he was moved by Fatma's entreaties and grief.
"In Desert and Wilderness"
Henryk Sienkiewicz
Every hour before it comes is darkened, every light is dimmed by its implacable shadow.
"Fortitude"
Hugh Walpole