Plot Summary

Will and Samantha (Sam) are a young couple expecting their first child. He flies from Seattle to visit her parents in Chicago, intending to ask her father Tom for permission to marry Sam. At dinner, he and Will get into an argument, and Will leaves without mentioning the pregnancy or wedding.The next day, Sam calls Will before his flight back. She gets scared when she hears a strange sound, and says, "Something's wrong" before the line goes dead. At the airport, all flights are canceled. There is a TV news report discussing preliminary reports on a seismic event off the West Coast of the US that has disrupted electrical power and telecommunication. Will returns to Sam's parents', where Tom and Will agree to drive together to Seattle to find Sam.Amidst heavy traffic, Will and Tom find soldiers have closed off the interstate. Invoking his prior service as a Marine officer, Tom persuades them to let his car through. That night, they are pulled over by a police car but the driver is in actuality not an officer, rather a civilian with a shotgun. The ensuing firefight results in an accident that fractures Tom's ribs. Tom knocks him out, and they use the police cruiser to tow their damaged car to a nearby reservation.At the reservation, mechanic Ricki fixes the car and agrees to travel with them in case they break down again. The trio set out, restocking provisions as they go. At one point, robbers hold the three of them at gunpoint, stealing their gasoline reserves. As being without fuel they are doomed, Will chases and catches up with the fleeing car. Ricki shoots out their tires, causing the vehicle to flip over. With the surrounding fire and the crashed car's leaking gas tank, they barely have enough time to take their gasoline back before the car explodes. Later that night, upset over what happened, Ricki leaves them.The next day Tom's lung collapses, so Will has to perform a needle thoracostomy. Sensing Tom will die without medical help, they bond, and Will finally feels that Tom approves of him and Sam. On a bridge, they encounter a gang of armed men on motorcycles. They work together to evade the gang, but Tom succumbs to his wounds. The car breaks down, and Will burns it so he does not have to leave Tom's body to rot. Will continues the journey on foot.A family picks Will up, and he leads them to his estranged father's empty house in Idaho where they all rest. He strikes a deal with them, taking their four wheel drive vehicle in exchange for them staying at his father's well-stocked house until they are ready to go north, where the situation is better. As he gets closer to Seattle, Will sees that the city is almost completely destroyed. The mystery thickens as Will notices dead victims buried in their cars under a thick layer of ash. Finally reaching Sam's devastated apartment, Will sees a note left by Sam with an address to a cabin.At the cabin, Will finds Sam with Jeremiah, a neighbor from the apartment building. Convinced the disaster is not natural but the result of an elaborate attack, Jeremiah reveals a deep paranoia. The next morning, he tries to kill Will, having fallen in love with Sam. Will shoots him in self-defense. Soon after, a volcanic eruption triggers a massive burst of fire, ash and shockwaves, causing a pyroclastic flow. Will and Sam speed away from the all-engulfing cloud, barely staying ahead of it but managing to out-distance it as it subsides. They proclaim their love for one another, regardless of what happens next, as they, too, head north. The cause and nature of the original 'event' are unexplained.