Sentence:  The foregoing , aided by several clues I 'll withhold to keep you on your toes , will pursue you with a tenacity worthy of Inspector Javert , but before they close in , gird yourselves , I repeat , for a <WSD>vengeance</WSD> infinitely more pitiless . 
Meaning of the word marked with <WSD> tags:  the act of taking revenge (harming someone in retaliation for something harmful that they have done) especially in the next life; I will repay, saith the Lord"--Romans 12:19