Secrets. We all got'em. We keep them in, we put them away, we let them die silent deaths one at a time. If they come back, we can attempt to hide them or we can do the right thing. Most movies are about the former, the machinations of characters struggling with themselves and outside forces. Locke is about the latter and all the fallout that happens.
Locke has left work and he won't be back for a bit. He's driving from his construction site to a hospital in London. He knows what lives there. He knows that making the trip will destroy his life, from his marriage to his job. And he does it all anyway, revealing his one big secret to person to person over the phone.
This movie is more than the sum of its parts. You might have even heard of it. It's the "Tom Hardy talking on the phone in a car for an hour and a half" movie. For the entire run time, we see Hardy sitting and driving. That's it. It's even at night so you can't say "oh look at the pretty English countryside." I'll tell you right now, it's compelling as all hell.
This is one of those movies that if I told you more of the plot, a bunch of you would scream "spoilers!" What works so much here, though, is I could tell you everything that happens and it's still damn good. Just a well crafted, well acted, solid piece of storytelling that doesn't hinge on a secret but the telling of that secret.