We’ve all done it. We know we shouldn’t. We know it is dangerous. Dwight (Mark Ruffalo) is racing to get his 10-year-old son home after a ball game went into extra innings. He is talking on the cell phone to the boy’s annoyed and anxious mother. And he is going too fast around the curve, just as his son slips out of his seatbelt to change the channel on the radio. Ethan (Joaquin Phoenix) has a 10-year-old son who is standing too near the edge of the road, freeing some fireflies from a jar.

And the unthinkable happens. A sickening thud. The driver’s son hits his head on the dashboard. And the car keeps going. The father speeds away, in shock and denial, seeing to his boy’s bruises and still trying to get him home on time, desperately, irrationally, magically thinking that maybe if his boy is safe, the other one will be, too.

But he is not. As Luke Arno (Eddie Alderson) is being returned to his mother, holding a bag of frozen peas to his swelling eye, the other boy’s mother and sister are huddled in the back of a police car, shattered by grief.