This paper offers a Kleinian analysis of Mark Twain's hostile depictions of the human conscience. Following a brief, initial consideration of such writings as Huckleberry Finn, A Connecticut Yankee, and What Is Man?, the paper focuses on the 1876 short story, “The Facts Concerning the Recent Carnival of Crime in Connecticut,” a fictionalized adventure in paranoia and manic defense against a persecutory conscience. A close reading establishes that while Twain's narrator displays all the paranoid-schizoid “hallmarks” as described by Melanie Klein (delusional omnipotence, splitting, paranoia, etc.), he also displays the capacity for guilt and remorse that Klein associates with the depressive position. In his retreat from that guilt he lapses into the paranoid-schizoid behavior associated with manic defense, and ultimately realizes the psychotic fantasy that concludes the story: the utter destruction of his conscience. This exegesis provides the first sustained Kleinian interpretation of Mark Twain's fiction.