In the film: The trapped survivors make it to a car and try to drive to safety, but the car runs out of fuel on a forest road. At this point, Thomas Jane’s David, shoots the survivors, including his young son, to spare them from a horrible fate. He runs out of bullets for himself, and walks out into the mist, waiting for death, only to find that the army’s come to help. It’s a brutal ending.

In the book: The book has a more optimistic ending. The survivors escape down a mist-shrouded highway, and they hear a safe destination spoken on a static-y radio, to give them hope.