A couple is brutally beaten in their home and the husband is killed. Mac rushes to the scene in time to get the wife to point out her attacker - her son, Billy Travers. Det. Flack immediately arrests Billy, who is shocked at his mother's accusation, and denies any involvement in the attack. Billy has no alibi and Mac thinks they have an open and shut case until Billy's mother recants her accusation. Further complicating things, and inmate at Riker's prison claims his cellmate confessed to the attack. Marvin Foster, who was serving a life sentence, escaped from prison and was recaptured the night of the murder near the Traver's home. Flack and Danny talk to Foster, who freely confesses to the crime and even tells them where he left the murder weapon but later find he lied. The team still suspects Billy but has no forensic evidence to support the case against him. Lindsay finds a unique type of glass chard at the scene which they trace to a local company whose employee, Paul Benson, used to live in the Traver's home. Paul was just released from prison after serving eight years for rape, primarily because his parent's testified against him. Paul wanted revenge but had no idea his parent's sold their home to the Travers. He attacked the Travers believing they were his parents. Mac finds Jo in his office looking through papers on his desk. Mac reassures her that what happened to her in D.C will not happen with this team. Jo opens up about the events which caused her to leave her post in D.C and both Jo and Mac gain a greater trust in one another.