Somewhere between a thriller and a clinical study in schizophrenia, "Keane" is a movie that puts you so far into someone else's head you may have forgotten your own name by the time it's over.

It's also the story of one of those marginal people on the periphery of urban life, so familiar to most of us, so willfully invisible to most of us. It's the bus station ranter: You know the guy -- he's always muttering madly to himself, he's always on the verge of an incident, he radiates hostility. You know enough to know that any encounter will be irrational, any transaction unsettling, any involvement disturbing, and you conclude: No, thank you. Then, eye-contact-free, you walk away.

"Keane" penetrates this poor pilgrim. In this case, he's possibly been unhinged by the loss of a daughter via abduction, enough to push any dad over the edge. But the director of the film, Lodge Kerrigan, doesn't clarify the situation. Did this really happen, did something worse happen, is it in his imagination, what? The awkwardness between knowledge and suspicion is extremely unsettling, particularly as we follow the damaged Mr. Keane (Damian Lewis, superb in "Band of Brothers" as Maj. Winters) during a few days of chaotic wandering in and around the Port Authority Bus Terminal in New York.

It's not an easy film to watch, and by the end, it's become a true ordeal. Kerrigan keeps the camera up tight on the man, following him through all his strained encounters in the real bus terminal. We see him beard baffled transit workers, attack a commuter, dip into and out of a series of lives. The movie turns particularly unsettling when Keane meets a woman who herself seems weirdly disconnected and out of contact. Clearly the survivor of some awkward domestic or legal situation, Lynn (Amy Ryan) is at loose ends in a transient hotel near the bus terminal. Keane tries to enter her life, but the exchanges are clumsy and uncompleted. Then she has a crisis (unexplained) and asks Keane to spend a few hours looking after her daughter, Kira (Abigail Breslin).

Knowing just a bit of Keane's story, we understand he has just passed into dangerous territory. The girl, of course, understands nothing. The film watches as the man struggles with his impulses, even if the nature of those impulses is unclear to us. Is he a father desperate to reach out or is he a molester feeling urges too profane for words.

That's suspense. That may be too much suspense for some, but it's vividly powerful.

Keane (100 minutes, at Landmark's E Street Cinema) is rated R for profanity, drug use and a sex scene.

As Keane, Damian Lewis plays a father ostensibly searching for his missing daughter.