Three months ago, Dominique Strauss-Kahn was one of the world's most powerful bankers and even had his eye on the Presidency of France. In a matter of weeks, he has been arrested, charged with serious sexual offences, forced to resign from his job and then suddenly, in a stunning reversal, released from his onerous bail conditions. By last weekend, the plot had begun to resemble a Greek drama with DSK as the victim of a miscarriage of justice, readying himself for the most astonishing of political resurrections in the final act.

Enter, stage left, a young French journalist called Tristane Banon. It isn't her first appearance in the piece but, just as one set of charges against the former head of the IMF appears to be on the point of collapse, she has taken over the role of his potential Nemesis. Two days ago, Banon filed a criminal complaint in which she alleged that Strauss-Kahn tried to rape her in 2002. This has been greeted with everything from total incredulity to a muted acknowledgement that assumptions about DSK's swift return to frontline politics in France were premature.

Why, demand his most loyal supporters, did Banon wait nine years to file a case? They believe that men like DSK, who are widely regarded as "grands seducteurs" in France, are vulnerable to false accusations by women who've misunderstood their intentions or exploited their weakness. This certainly isn't how it looks from the standpoint of people who work for organisations that support victims; the disbelief that has greeted Banon's complaint is common in sexual assault cases, reflecting a series of mistaken assumptions or "rape myths" about how victims behave.

First, it's not unusual for victims to wait years before they feel able to report their experience; in this instance Banon confided in her mother Anne Mansouret, a Socialist councillor, at the time of the alleged assault. DSK was a hugely powerful figure in the French Socialist party, a former finance minister and potential presidential candidate, and Mansouret talked her daughter out of making a formal complaint, a course of action she now says she regrets.

But in 2007 Banon appeared on a TV show and said she had been attacked five years earlier by a politician whom she went to interview at his apartment. DSK's name was bleeped out on transmission, but it is clear that Banon's accusation long pre-dates his arrest on sexual assault charges in New York.

Nor is it unusual for victims to take action only when events appear to suggest that another woman has been attacked by the same assailant. It's often only when a woman realises that her experience wasn't an isolated incident that she goes to the police. In the most extreme British example, more than 100 women have come forward to identify themselves as possible victims of the Black Cab rapist, John Worboys, since he was convicted of attacks on 12 women in 2009.

Police or prosecutors sometimes decide an alleged victim wouldn't make a good witness, but that doesn't mean an assault didn't take place. Le Monde reported yesterday that the director of the Crime Victims Treatment Centre at St Luke's-Roosevelt Hospital in Harlem, who examined DSK's first accuser on the day of the alleged assault, found her "in a state of shock, very shaken, very affected.... I didn't doubt her testimony". It now seems unlikely that events in Suite 2806 at the New York Sofitel will ever be scrutinised in court, which is the proper place for such conflicting accounts to be tested. Instead, attention has switched to Banon, whose mother says she took the decision to file a complaint against DSK after "maturely reflecting". The messy drama has yet to reach its finale, but DSK would be foolish to underestimate his latest adversary.

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