CARL COLBY is the son of William Colby, an intelligence operative who became director of the CIA during the Nixon and Ford years. Carl's documentary The Man Nobody Knew is the fascinating, maddening biography of a father whose career centered on secrets. "He didn't have a lot of romantic ideas about spying," Carl narrates. "He saw it for what it was: dirty business."

There are two huge stories tugging at either end of Carl's film, and the result is that it feels like a compromise of each. There's the gargantuan story of American intelligence, in which warfare and diplomacy bred new tactics during the Cold War and Vietnam. An irreconcilable paradox emerged: The CIA's immense catalog of secrets needed to be both exempt from oversight by the nation at large, and—as part of the democratic system—fully accountable to it. There's gripping footage of William's numerous Congressional hearings, in which we see him grappling with secrets in front of a panel that demanded total transparency in the aftermath of Watergate.

The other, more personal story in The Man Nobody Knew is the one that the filmmaker is uniquely qualified to tell: that of an inscrutable father. His sister Catherine died at a young age after struggling with epilepsy and anorexia, and it's suggested that William took her death very hard. William also, out of nowhere, divorced his wife, Carl's mother, and Carl doesn't really know why, nor does he venture a guess.

William Colby was replaced as CIA director by George H.W. Bush, ushering in our current era of cronyism in American intelligence. As for William, he died mysteriously on his boat; murder, suicide, and natural causes have each been theorized. Carl, for his part, picks one, but the resolution is unsatisfying. Such is the nature, perhaps, of a film about an unknowable man.