Steve Martini's Undue Influence (1996)

Based on the book. A criminal attorney defends his hotheaded sister-in-law who's accused of killing the trashy new wife of her ex-husband, a shady U. S. senator. Refusing to help her own case, her determined brother-in-law must piece together a viable defense while dodging a vengeful hit man. He slowly uncovers a government cover-up, political corruption and the fact that his innocent client has been protecting her tormented teenage son, who shot his promiscuous stepmother after she repeatedly seduced him.