When mum Sharon Thompson saw an old man behaving suspiciously with a teenage boy in a parked car, she was horrified - and then incensed.
She was so sure the man was up to no good that she drove her car alongside them. And then the look on the lad's face said it all: he was being abused - and he needed help.
Appalled Sharon, 44, chased the paedophile for two miles, while giving police a running commentary, and she has now been praised by a judge after pervert Martin Harness was convicted of 'sexual activity with a boy under 16'.
Sharon and boyfriend Elliott Cox were out shopping when they spotted the man in a car park.
Sharon, 44, said: "It was clear something was going on. We pulled up alongside and the boy had a look that said 'please help me'."
As they called 999, the pervert drove off with the scared lad still in the passenger seat - so they followed.
Elliott, 45, said: "We had to. There was no way he was going to get away with what he had done."
Sharon described the route to the operator by reeling off street names on her mobile. Waiting officers then swooped on pensioner Martin Harness, 67, in Hull, East Yorks.
Mum-of-six Sharon said: "They dragged him out of the car. That kid had a look of fear. He didn't want to be there."
A judge at Hull Crown Court awarded the couple £250 each as Harness, of Grimsby, admitted sexual activity with a boy under 16. He got three years' supervision and a sexual offences prevention order.