A hostage situation at a supermarket changes everyone's lives.
Susan declares her love for Ian; Gaby and Carlos try to regain what they have lost; Bree must confront Orson's past.
After a mass murder at an Internet security company, evidence indicates that the person responsible is not a typical serial killer; Prentiss is required to complete recertification training.
Torres and Lightman question a former gang leader who claims to be rehabilitated; Loker and Foster look into the death of a firefighter who was killed in the line of duty.
Beckett races to find a stolen toxin capable of killing thousands of people; Castle has less than 24 hours to live after being exposed to the chemical weapon.