Amnesia has been a staple of movies since time immemorial, but few, if any of them have cut to the bone the way this modest documentary by Rupert Murray does. “Unknown White Male” tells the frightening, yet fascinating story of Murray’s acquaintance Doug Bruce, a well-to-do British photographer living in New York City who suddenly found himself on the subway without any memory of who he was or what he was doing. The film recreates his experience of going to the police and hospital for help, gradually discovering–or rediscovering–his still-mysterious past, and reconnecting with the friends and family he doesn’t recall in the slightest. The most affecting part of the picture is watching Bruce emerge as a new person, confronting the world with a sort of childish innocence and exuberance that contrast with his previous rather cynical frat-boy character and seeming to those who knew him before the onset of the condition a very different man. But the interviews with those who must acclimate themselves to the changed Doug, and with medical and psychological experts who comment on what Bruce’s condition might be, prove telling counterpoints to the footage dealing with Doug himself.

There’s been some suggestion that Bruce has been faking his amnesia, but if that’s the case, he’d have to be congratulated on his persistence (the con, if that’s what it is, is now in its third year) and his thespian ability–the dazed reaction with which he tries to make contact with his father, sisters, and chums from back home is extremely convincing. His sadness at being unable to get to know his mother–whose recent death, it’s suggested in passing, might have been a key to his loss of memory–is particularly affecting.

Though “Unknown White Male” is essentially a single case study, it inevitably raises the broader issue of what makes a person who he is–whether we are all, in fact, our memories, and whether we cease to possess an identity at all if we lose them. In other words, is Doug the same individual he once was, or is his process of “reconstruction” through new experiences making him a “new man” in the most fundamental sense? It’s the sort of provocative question that makes the film, narrated with suitable blandness by Murray (who’s as distanced from Bruce now as all his other old acquaintances are), the sort of effort that’s likely to engender a good deal of serious discussion among viewers afterward.

And that’s always a sign of a documentary that’s worth seeing.