There are certain accusations of rape so spectacular that a huge number of people, when they hear about them, are driven to pour out grief and anger—the high-school girl in Steubenville, Ohio; the three women trapped in the Cleveland house of horrors; the young woman gang-raped in Delhi. The women’s ordeals seem to belong, for a time, to everyone: newspapers and social media carry the developing stories while the public tries to understand. But there is another category of rape accusation—when a long time has passed since the alleged event, and, most important, when it happens within a family—that incites more fitful, ambivalent expressions of outrage.

An “open letter” in Sunday’s Times reawakened a case that is more than two decades old—once famous but in many quarters half forgotten. The alleged victim, who is now twenty-nine, is Dylan Farrow, the adopted daughter of Mia Farrow and Woody Allen. She wrote on Nicholas Kristof’s blog, with the kind of vivid, absorbing detail that is hard to get out of your mind, that she had been sexually assaulted by Allen when she was seven years old:

My father took me by the hand and led me into a dim, closet-like attic on the second floor of our house. He told me to lay on my stomach and play with my brother’s electric train set. Then he sexually assaulted me. He talked to me while he did it, whispering that I was a good girl, that this was our secret, promising that we’d go to Paris and I’d be a star in his movies. I remember staring at that toy train, focusing on it as it traveled in its circle around the attic. To this day, I find it difficult to look at toy trains.

The open letter is wrapped up in all the tangled plotlines of the past two decades. Woody Allen had an affair with Mia Farrow’s adopted daughter Soon-Yi Previn, when she was nineteen or twenty-one (her official date of birth is uncertain) and he was fifty-six (they later married). The affair precipitated Farrow and Allen’s separation and an acrimonious custody battle over their three shared children, in the midst of which Allen allegedly molested Dylan. A criminal investigation was initiated in Connecticut, but the charges were dropped when a judge deemed the investigative team’s findings inconclusive (though Farrow was granted custody of the children). The Connecticut county prosecutor who presided over the case insists that he had “probable cause” to believe Dylan but decided against pressing charges “rather than exposing the child to possible harm.”

Alongside this knotty legal accounting, we have the procession of Allen’s films—one a year since 1969—many of which brilliantly explore dark fantasies about family life, sexual life, aging, and moviemaking. Then we have Allen’s persona as the perpetual analysand, so aware of his own neuroses and perversions, so willing to confess and discuss and make use of them in his acting, directing, and writing, that curiosity about his private life is preëmpted: it’s all there in the work, transformed into art. You can read this as a cleverly defensive posture, or as the fearlessness of a truly liberated soul with nothing to hide from himself or from his audience.

The accusations have not been proven in court, and Allen has vehemently denied them, issuing a statement on Monday that Dylan’s article is “untrue and disgraceful.” Since Dylan’s piece was published, battle lines have been drawn. Some have lauded Farrow’s courage in telling her story. Others—including, most recently, Dylan’s adoptive brother, Moses—have argued that Mia Farrow manipulated her daughter and seeks revenge and attention. Still others, including the public editor of the Times, have criticized the strange presentation of the story, bracketed by Kristof’s personal imprimatur and a disclaimer that he is a friend of Mia Farrow and her son Ronan. (Allen has had a long association with The New Yorker.) An oddly dominant part of the discussion has been about art, and how our judgment of Allen’s films should or shouldn’t be influenced by this alleged cruelty in his personality. A typical sentiment: “Damn it, does this mean I have to stop watching his movies?”

This kind of squirming seems like a way of avoiding a larger topic: the still-hidden subject of rape within families and how frequently it takes place. (According to a study by the Rape, Abuse, and Incest National Network, in about a third of juvenile-assault cases the attacker is a family member.) The public attention given to sensational rape cases in recent years has usefully spotlighted the conservative and misogynist social norms that give cover to rapists, as in Delhi, and, as in Steubenville, the sports culture that lionizes teen-age boys and seems to put them beyond the law, and the ways communities shame victims. It’s much rarer to see a big public airing (except perhaps in the realm of TV melodramas) of a sexual assault that takes place within a household.

Many people writing about the case have essentially said, “We don’t know what really happened.” In qualifying the discussion, they are upholding the American right of innocent until proven guilty. But they are also upholding another difficult-to-combat belief: that what goes on within the confines of family life, especially a family life as messy and complex as the Farrow-Allen household’s, is essentially unknowable and private. That each member of a family has his or her own idea of what occurred, and that all of these stories have some bearing on the truth—and that the real truth, if there is such a thing, may be unrecoverable.

The complexity and frequent pain of family life can be difficult to understand even for members of a family, who were there. How much more opaque must it remain for people outside the household, who can’t see what goes inside? When we ask how we can ever know what happened, we are, to some extent, repeating an old-fashioned cliché: “It’s not our business.” On this point, some crucial sentences by the feminist academic Phyllis Rose come to mind, from her 1983 book “Parallel Lives,” a history of five intense, often bizarre, sexually complex marriages. Rose explains, in the introduction, why a history of the private lives of five families in the nineteenth century is really a book about politics: