A young married couple gets stuck in a traffic jam while on their way to the pregnant wife's mother's house to deliver some groceries. When a loud bang rings out, the wife tells her husband the sound was a gunshot and that she just saw an old man - one lane over and a few cars back - kill his passenger. She's certain he saw her and will now try to kill her too!
Their cell phone battery dead, they try to get help from the driver of the car next to them, but he just thinks the wife is nuts. As the jam opens up a little, the gunman does manage to get beside them and shoot - shattering the passenger-side window of the couple's car. Fortunately, the pregnant wife had ducked down in time. The traffic opens up some, and her husband guns the engine, leaving the shooter behind.
Finally, one lane over and a few cars ahead of them, a police cruiser! They have to get his attention. The woman starts throwing what she can find at the police car - an old flashlight from the glove compartment, the dead cell phone. Finally, she digs into the groceries. When she is able to hit the police car with a couple of eggs and a small sack of flour, the officer live parks his cruiser and gets out to confront them.
They warn him about what is going on, and the officer is able to arrest the shooter. The woman he killed was his wife, and he was after her insurance money in a fake-murder plot gone wrong.