Furious that his 14-year-old son had been buying cannabis, Cenydd Nickels vowed to bring the dealer to justice.
His anger was made worse by the fact his mother had recently been violently mugged for the sake of just £6 to buy drugs.
But when the 53-year-old tracked down the culprit and carted him to a police station, officers were not interested.
They let the suspect walk free...and put Mr Nickels in the dock instead.
Their decision triggered a five-month, £100,000 legal battle that ended only when the Crown Prosecution Service decided to drop the charges without explanation.
Mr Nickels had confronted the drug dealer in a ‘sting’ operation at a park, having been promised by police they would be there to make an arrest.
No officers arrived and – following a fight – Mr Nickels, who is a dog warden and junior rugby coach, put the younger man in the boot of his car and drove to a police station.
The station was closed so he telephoned officers who arrived 20 minutes later.
To Mr Nickels’s horror, they arrested him for assault – even though the dealer told them he did not wish to press charges.
The next day he was charged with kidnap and causing actual bodily harm.
That led to ten court appearances until, at Swansea Crown Court last month, prosecutors decided to offer no evidence and he was formally acquitted of both charges.
One of his neighbours in Ystradgynlais, near Swansea, said: ‘Cenydd is a pillar of our community.
‘He’s there for young people week in week out at the rugby club and is well known in the area for being a lovely guy.
'No one here will have a bad word to say about him. It’s a joke that he was arrested in the first place. What a waste of everyone’s time and money.’
Mr Nickels posted an emotional message on Facebook about his arrest in January.
In it he said his mother had been left black and blue by her mugging ordeal and needed hospital treatment, including stitches, for her injuries.
He added: ‘I would like to take this opportunity to thank my family, county councillors, community councillors, scout leaders and the people who have supported me over the past few weeks.
‘We have won the battle, but not the war over drugs in our community. We must stick together and keep on top of the drug dealers and report them to the police, so that they will always be looking over their shoulder in future.