Theo James plays Will who is the partner of Sam and they live in Seattle. Sam is pregnant and Sam's dad doesn't much like Will. There's a anxious opening when Will visits her parents while on a business trip to Chicago and this tension sets the scene for what's to come between the two main leads. Sam's dad Tom is played by Forest Whitaker. He's an ex-military man and clearly no man is going to be good enough for his daughter, particularly when he is instrumental in resettling her thousands of miles away from her parents.
Whilst in Chicago, the event happens. They soon lose communication with each other and so proud dad and loving partner head off by road to 'rescue' Sam, even though they can't know where she is by then, or even if she is alive. The film then turns into a road-trip with the two of them in the car trekking across distance and the focus of the film is survival of this trip (or not) and the mini-adventures they get into along the way.
There are lots of these adventures of course, each an incident of their own, as they come across situations and people who are equally lost and numb, others beginning to make provision and get organised but many just disorientated and often dead. As far as they all know this could be the end of the world - How It Ends, maybe. Much of the film though is about the changing relationship, learning and evolution of the relationship between the two men. How they start off with that anxiety I mentioned, then end up in a position of mutual reliance in order to survive and reach the girl they both love.
Interesting visually with harrowing landscapes sets which are convincing and they got the pacing of the story just right. The acting by the two leads is convincing, and indeed those around them. Anyway, it's on Netflix UK just now and I think it's well worth a look.
Spoiler alert: There isn't really a clean ending to the film. This has got considerable bad press from those expecting every film to have a neat Hollywood ending tied up with bows, but I think that this reflects the nature of what is going on and helps to place the audience into the shoes of the characters facing this thing, whatever it is. It also leaves it open for some bright spark to make a sequel, I guess! I dread to think how people these days would cope with films like Hitchcock's The Birds!