In March of 1909, Mark Twain cheerfully blessed the wedding of his private secretary, Isabel V. Lyon, and his business manager, Ralph Ashcroft. One month later, he fired both and wrote a 429-page rant calling Isabel "a liar, a forger, a thief, a hypocrite, a drunkard, a sneak, a humbug, a traitor, a conspirator, a filthy-minded and salacious slut pining for seduction." In Twain's End, Lynn Cullen reimagines the tangled relationships that transformed Isabel Lyon from beloved secretary into a woman Twain was determined to destroy.