Their paths crossed for precisely half a second during the evening rush hour at Waterloo Station.
Mark Pearson, a 51-year-old artist, was on his way home from work, weaving through a thick tide of London commuters.
Walking towards him across the concourse came an award-winning star of film, TV, theatre and radio. She had just been to a yoga class and was heading to a rehearsal. Neither knew the other.
What happened next - or rather what didn't happen - would cast Mr Pearson into what he calls a year-long "Kafkaesque nightmare" from which he has only just escaped, and for which he squarely blames the Crown Prosecution Service.
It cannot be said with certainty that the artist and the actress made even fleeting physical contact. CCTV images showed only that they walked past each other.
Yet the woman, who is in her 60s, claimed Mr Pearson sexually assaulted her - penetratively - for "two or three seconds".
This was followed, she insisted, by a violent blow to her left shoulder. Images of the moments before and after they passed were captured from CCTV and shown to a jury during Mr Pearson's three-day trial at Blackfriars Crown Court in London last week.
They plainly demonstrated, his lawyer Mark Bagshaw said, that the allegation was not true. How could it be, he asked, given the half-second time frame? Indeed, the images showed his client walking at a normal pace. He never broke stride.
What's more, in his left hand - the one which he is supposed to have used to assault the actress - Mr Pearson carried a newspaper. His right hand gripped his bag.
Mr Pearson told the court: "I would have had to crouch down, put my hand up the woman's skirt... penetrate her, take my hand out again... all while holding the newspaper and walking along the concourse... It's preposterous... It is against everything I believe in as a human being. I did nothing."
There were no witnesses and no forensic evidence. The actress failed to pick out Mr Pearson in an identity parade of video images.
Summing up the case, the judge, His Honour Peter Clarke QC, told the jury that to convict Mr Pearson they had to be sure the assault happened as the actress described.
It came as little surprise to Mr Pearson - though he was profoundly relieved and grateful - when the jury of nine women and three men unanimously rejected the woman's story after deliberating for little more than 90 minutes.
What he cannot understand, what still gnaws at him when he wakes up at 4am, his body shaking, is why the case reached court in the first place.
"One of the many frightening aspects is that this could have happened to anyone," he told The Mail on Sunday yesterday.
For me, half a second turned into a year of hell. I feel I have undergone a form of mental torture sanctioned by the state.
Every day, some 300,000 people flow through Waterloo in Central London - Britain's busiest station. "I was just one of those commuters - in the wrong place at one moment in time," he said.
It goes without saying that the actress will remain anonymous. The law doesn't afford the same privilege to Mr Pearson, who has undergone cognitive therapy for anxiety attacks brought on by the stress.
But the greater part of his anger is directed at the CPS, which, having assessed the evidence, decided to charge him with "sexual assault by penetration". He said: "It is just bizarre. Why couldn't the CPS have used common sense?"
Over the past year and more, the CPS has been repeatedly stung by criticism of its decision-making in a series of high-profile sex cases.
At the same time, it has sought to deal with concerns that many women are put off reporting rape and sexual assault because they lack faith in the justice system.
Mr Pearson wonders whether he is "a victim of the way the CPS is rigorously trying to redress the balance". One of his supporters, author Erin Pizzey, the family care activist who founded the world's first shelter for victims of domestic violence, certainly believes so.
"The CPS have recently been wrongly targeting men and it has got to stop," she said. "The CPS had no business going after him [Mr Pearson] because there wasn't a case there from the very beginning. At the moment, women seem above the law. They can do it in domestic violence cases - simply pick up the phone, no evidence required, and have a man removed from his family and his children - and they can do it with rape, too."
The CPS said: "There was sufficient evidence for this case to proceed to court and progress to trial. We respect the decision of the jury."
Mr Pearson's ordeal began on February 5 last year, two months after the "incident", when he was arrested at his East London home. Police traced him through data retrieved from his Oyster travel card.
He was "dumbfounded" but readily co-operated with police, ignoring advice from the duty solicitor to say nothing. He was happy to answer their questions and clear up "this obvious mistake". He said: "I was convinced good sense would prevail."
He told police that he remembered nothing of that evening on December 3, 2014. The artist was returning home through Waterloo as normal from his work as a picture framer.
Four months later, his solicitor rang his mobile to say he was going to be charged. "I was on a Tube train and I staggered off in a daze," he recalled. "It felt completely bizarre."
As the months dragged by this feeling gave way to terror.
"It is horrible and frightening to contemplate going to prison for a crime you haven't committed. Particularly a sex crime. We have all heard about how sex offenders are treated in prison."
His partner, Carol Ho, 41, whom he met at the Royal College of Art, said: "It was a very stressful time for Mark. None of us believed for a second that he was capable of doing what this woman said. It was all crazy."
The actress's interview with police was shown to the court at the start of his trial. The moment she was attacked came, she said, after he "clocked" her and smiled, and gestured with his newspaper for her to pass by. "The next thing I know, his hand is up me.... and then I felt this enormous blow on my left shoulder." The court heard she was wearing a coat and jacket and a thin dress over "training pants".
She said: "I staggered and yelled... and people just stopped all around me, and I was looking back after him." Then she said he "shot off... legging it towards the ticket barriers" - although the CCTV images shown to the court demonstrated this was not the case.
It was only halfway through her interview with police that she described in detail the way in which she claims she was sexually assaulted. In his summing up, the judge said she had seemed "coy" about this aspect of her account, that she had seemed to dwell more on the alleged blow to her shoulder.
Instead of continuous film, the station's cameras record one image per second. Forensic scientist Jacob Blythe, who compared the pictures with the woman's statement, told the court that Mr Pearson passed the actress for "half a second".
In a report prepared for the defence that was not shown to the jury, he said the CCTV footage did not show Mr Pearson touching his accuser "in any manner". He added: "I consider the imagery unsupportive of her claim that 'his hand was up me'."
Mr Pearson told The Mail on Sunday of recently watching a TV programme about the Witchfinder General, who tortured confessions out of suspected witches during the English Civil War. He said: "The narrator said, 'Imagine living in an England where you could be hanged on the hearsay of a neighbour.'"
"Sadly, I can imagine this all too easily."