Sentence:  Then, just before the wedding, the old man feels he's honor bound to tell his future son-in-law the secret of his past; so the damned idiot <WSD>blathers</WSD> the whole story of his killing the man and breaking jail! 
Meaning of the word marked with <WSD> tags:  To say (something foolish or nonsensical); to say (something) in a foolish or overly verbose way.