In the novel Sudden Mischief, private investigator Spenser is asked by his partner, Susan Silverman, to aid her ex-husband, Brad Sterling, who is facing a sexual harassment lawsuit. As Spenser investigates the claims, he discovers that Sterling is entangled in a far more dangerous scheme involving charity fraud and a money-laundering operation linked to the mob. The situation escalates when a murder victim is discovered in Sterling's office, prompting a hunt for the truth that puts Spenser and Susan in the crosshairs of ruthless criminals like Haskell Wechsler. Through confrontations with corrupt lawyers and dangerous enforcers, Spenser gradually uncovers how Sterling’s personal debts and professional deceptions led to a violent web of betrayal. Ultimately, the narrative explores the complexities of Susan's past and the psychological burden of her former marriage. The story concludes with Spenser resolving the criminal threats while helping Susan confront her history and reaffirm their partnership.