A couple meet at a party. They drink rather more than is good for them. He takes her back to her room. They sleep together.
The next morning, though she cannot remember exactly what happened, she says she would never have agreed to sex with a man she has only just met. Maybe, he replies, but she certainly consented to everything that happened between them that night.
She tells the police she has been raped. They explain what she must prove in court. It is not as simple she might have thought from the recent Home Office publicity campaign.
First, there is the physical act of penetration - broadly defined these days, but not denied in the present case. Then, there must be proof that she did not consent to the penetration. And, finally, the prosecution must prove that he did not reasonably believe she had consented.
"I am sure I didn't consent," she tells the police - and the case goes to court.
Under cross-examination, though, a different picture begins to emerge. She admits that she was so drunk that she could not remember what happened. For all she knows, she might have given consent. She certainly cannot remember saying "no".
But even if she did say "yes", she says she didn't mean it. She was so drunk that her consent should have counted for nothing. He must have known she was in no position to agree to anything.
Broadly speaking, those were the issues that lay behind the prosecution of Ruari Dougal, 20, a student from Co Donegal who was working as a security guard at the University of Aberystwyth. At Swansea Crown Court last November, he was acquitted of raping a fellow student, aged 21. And then the heavens fell in.
Vera Baird, QC, an unpaid parliamentary aide to the Home Secretary, expressed "outrage" at the decision of Mr Justice Roderick Evans to direct an acquittal.
By next morning, Mrs Baird was passing judgment on the judge. "He is wrong," she said. "There is no doubt about that: it is a dreadful error. The judge is utterly and totally wrong. He needs to be spoken to and sent on some re-training." That was a remarkably offensive remark for anyone to make about a High Court judge. For a politician who aspires to a job in the Home Office, it was particularly inappropriate.
So it was even more remarkable to hear similar sentiments expressed by one of the Government's law officers at a press briefing last month. Mike O'Brien, MP, the Solicitor General, said he would want cases such as the one in Swansea put to a jury rather than stopped by a judge.
Again, Mr O'Brien seemed to be suggesting that Mr Justice Roderick Evans had somehow got the law wrong. And that view was reinforced by a comment about the case in a consultation paper issued by Mr O'Brien and colleagues at the Home Office and the Department for Constitutional Affairs.
"What was not addressed at the trial was whether or not the victim had the capacity to consent to sexual activity given her level of intoxication," the paper said. "It could be argued that these were matters that could quite properly have been put before a jury and the matter left for them to decide whether or not the complainant's level of drunkenness had meant that she was not capable of consenting to sexual activity."
This all struck me as rather odd. As the local news agency accurately reported, the case was stopped because Huw Rees, prosecuting, decided to offer no further evidence. Surely, that left the judge with no option but to direct an acquittal? What else, I asked the Solicitor General, could the judge have done?
That was not the sequence of events, Mr O'Brien explained. There had been discussions between the prosecutor and the judge and it was only after these had taken place that Mr Rees accepted the judge's view of what had happened.
Really? Nobody had suggested until now that the judge had put the prosecutor under any pressure. I asked Mr O'Brien's office for a transcript of the judge's remarks. This shows that the decision to drop the case was made by counsel, as one would expect.
The judge certainly agreed with it. He went further, heavily criticising the Crown Prosecution Service for bringing a "wholly unrealistic" prosecution and saying that he would probably have stopped the case himself if counsel had not done so. But there were no discussions in court.
To Mr O'Brien's credit, he rang me to acknowledge that his recollection had been wrong when he had briefed reporters earlier in the day. The law officer had been thinking of the discussions between the judge and counsel after the acquittal.
But Mr Justice Roderick Evans had still thought it right to stop the case. Was this a "dreadful error", as Mrs Baird alleged? Surely not? The judge's view was that no jury, properly directed, can convict a defendant of rape unless the prosecution can prove that the victim did not give her consent. That could not be established in this case.
True, there are "evidential presumptions" that an unconscious victim cannot consent. But the Government is not proposing to extend that presumption to cases of intoxication, since it is not regarded as difficult to disprove the presumption.
Defining "capacity" strikes the Government as a better way forward. A person consents to sexual activity only if he or she "agrees by choice, and has the freedom and capacity to make that choice". So, if a woman does not have the capacity to make a choice, she cannot be said to have consented. Provided ministers can come up with a definition of capacity that excludes those who have been drinking heavily, it would be possible to show that the woman was never sober enough to say "yes".
But how can you possibly establish that anyone, while still awake, is too drunk to consent? Breathalysers in the bedroom? And where would you set the limit? Are we really telling couples they cannot have a few drinks without one of them risking life imprisonment? How can anyone prove that she did not briefly sober up and give her consent?
There are good reasons for not changing the law, as David Blunkett explained in 2002: "I have rejected the suggestion that someone who is inebriated could claim they were unable to give consent - as opposed to someone who is unconscious for whatever reason, including because of alcohol - on the ground that we do not want mischievous accusations."
For once, the Home Secretary was right.