Meredith and Lexie's father returns to Seattle Grace with stomach pains and a new girlfriend; Alex butts heads with the new OB; Mark bribes Jackson for information on Lexie.
The team heads outside the hospital to help provide medical attention at the scene of an emergency.
Rookie cop Ben Sherman wonders if he is cut out for the job; a girl is kidnapped.
As July Fourth dawns, the cell prepares to launch two coordinated dirty bomb attacks on the city of Los Angeles, while Darwyn and the FBI move to shut them down.
An unidentified woman is found dead in an alley; Nate's little sister goes missing and secrets from his past unfurl.