Sentence:  The Bat—they called him the Bat. Like a bat he chose the night hours for his <WSD>work</WSD> of rapine; like a bat he struck and vanished, pouncingly, noiselessly; like a bat he never showed himself to the face of the day. 
Meaning of the word marked with <WSD> tags:  Sustained effort to achieve a goal or result, especially overcoming obstacles.