When a huge building collapse traps one of Mary's witnesses under the rubble and out in the open, his injury plays second to the threat of a professional assassin up on the roofs.
An Orthodox Jewish witness, whose estranged wife refuses to enter WITSEC, soon finds himself being followed by a mysterious man (guest star Richard Schiff) who answers to a higher authority.
When Stan's first witness turns up dead, with his badge amongst the bones, he becomes the chief suspect - forcing Mary & Marshall to dig deeper into a 20-year-old love triangle.
When a bridge collapses and plunges many to their death, the victims' families come after the engineer, who, once in WITSEC, attempts to clear his name no matter what the consequence.
When a series of murders seem to follow a new ex-con witness, including stabbing Mary's friend, she and Marshall have to figure out if he's the killer in time to save his next victim.
