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.