"Jonas and Bob steal top-secret documents in Hong Kong, but their escape route via subway is disrupted when the city's trains are unexpectedly shut down and the military is called in to search and question everyone aboard. Back at home, Molly is kidnapped and comes face-to-face with renegade Sam. Mack and Tiffy desperately search for Lissy after she disappears from a local shopping mall."

"Molly is kidnapped by Sam and used as bait to prevent Jonas and his team from capturing a Russian terrorist cell that is planning to bomb several U.S. cities. Meanwhile, Kim calls the police and reports Molly missing, complicating matters for the Unit."

"The fourth season concludes with the team attempting to track down and diffuse three nuclear bombs that are targeted for undisclosed locations across the U.S., and Col. Ryan is shocked to learn who is really behind the attacks. Meanwhile, Molly informs the other wives that she is leaving Jonas; and preparations are made for Grey's wedding."