I finally got the chance to watch last Sunday's episode off of the HD-DVR.
The Unit and their families were scattered around their community when chlorine gas leaked into the water system, poisoning everyone outside and cutting off communication with the outside world.
Tiffy, who was supervising detention at the school, managed to seal off the classroom and protect the students with her. Grey was on the road but secures a number of other drivers in the back of a closed refrigerator truck. Mack, his kids, Molly, Kim and Bob quickly made it back to their apartment building where they aided other residents to safety. Mack and Bob later found a neighbor's scuba equipment and used it to make it to the Aerodyne offices where they found Jonas and Sam, both of whom were the only ones with outside communication
They eventually located the water plant where the chlorine gas was inserted into the system, took down the apparent terrorists there and shut off the release of the poison. Colonel Ryan later informed the Unit members and their families that the incident appeared to be a test run from the terrorist group they'd been investingating since the season premiere and that they'd be relocated, with Bob and Kim to be reunited with their children.
Next week: the Unit fights to rescue Jonas's old friend even with a broken helicopter gas tank and nearby guerillas impeding the mission. Also, Colonel Ryan goes to extreme measures to extract information from a recovering alcoholic whose husband may have been behind a terrorist attack.
-G