One summer night in Kansas four teenagers are out joyriding; the driver turns off the headlights because the air is filled with lightning bugs, a fantastic sight. And then the car plows into a combine stalled on the road. Cut to four years later, when the driver, Chris Pratt (Joseph Gordon-Levitt), now brain-damaged from the accident, is working as the night janitor at the local bank and sharing an apartment with another damaged man, the ex-con Lewis (Jeff Daniels), who was blinded by the fumes in his own illegal meth lab. Chris has great difficulty remembering; where is the can opener? Where are his car keys? (Left in the locked car once again, but he has been careful to keep another key in his shoe for just such emergencies.) He keeps a notebook to remind himself of everything from appointments to people's names to pickup lines he overhears. Long conversations, particularly with emotional overtones, and particularly with his parents, trigger his guilt and frighten him into running away.

He's hopeful that the bank manager will let him learn to be a teller, but that seems a forlorn hope, since keeping track of things is so difficult for Chris. But then he runs into an old high-school acquaintance, Gary (Matthew Goode), who seems to know a lot about him, brings him into his own group, introduces him to a pretty young woman, flatters him, and then invites him to help rob the bank he works at by being the lookout during the heist.

That's the setup of "The Lookout," and it's fresh enough to show us the talent and invention of its writer-director Scott Frank, who made his reputation as a screenwriter with "Out of Sight" and "Get Shorty." But unlike those films, this is not a comedy; Frank takes time here to tell a serious story, and lets it breathe, and yet he doesn't make us wait for things to happen; he trusts the skill of his script, his actors and the documentary-like camerawork of his cinematographer Alar Kivilo to carry us along. And up until the ending, the film constantly surprises us and defeats our expectations; it's marred only by a too-familiar ending that echoes a couple of films we've already seen.

But "The Lookout" has a wonderful leading actor in Joseph Gordon-Levitt as Chris, who plays without a hint of self-consciousness. Though his character has built a shell around himself, he must stay focused on every single action of his day and his life; he has to think about all the things the rest of us take for granted, and as an actor Gordon-Levitt lets us see right into him every moment of the film. I was reminded of his work as a gay hustler in Gregg Araki's powerful 2004 film "Mysterious Skin," which was a profound look at the endless pain, lasting into adulthood, of child sexual abuse. In "Mysterious Skin" Gordon-Levitt's character again has a shell - a different kind of shell - around his emotions; but again he has the ability to let us see through it into his heart. In a bad season for movies this spring, "The Lookout" will go on my list as one of the most worthwhile films of the year.