Four motor scooter riders went to look for a man one of them had collided with in a park and beat him up.
They might have got away with it had one of them not lost his phone in the fight - for when Tan Wee How later tried calling his own number, it was answered by a police officer.
All four were swiftly arrested and, yesterday, they were sentenced to jail for attacking Mr Roman Barros Griffiths, 45.
The Argentinian was walking with his wife in Bishan Park 1 late on Feb 10 last year when the four men rode towards him after sharing four bottles of beer at a coffee shop.
He raised his arm to signal them to stop so that he and his wife could cross at a junction.
But they rode past and the final rider, Ng Yeow Tim, 40, bumped into Mr Griffiths' arm.
An angry Ng then confronted Mr Griffiths and an argument broke out.
The court heard that they exchanged angry words before Ng rode away and told his friends what happened.
They decided to look for Mr Griffiths to settle the score and spotted him about 10 minutes later.
When Ng shouted at him, Mr Griffiths said he would call the police.
Tan suddenly ran towards the Argentinian and punched him in the head three times.
Mr Griffiths tried to escape but the three other attackers caught up with him, punching and scratching him before he eventually managed to break free and called the police.
Tan also kicked Mrs Griffiths' leg when she told the group to stop the attack, causing her to fall.
When the men had fled, she found Tan's phone, which she handed to the police.
Deputy Public Prosecutor Teo Lu Jia said: "When Tan called his own mobile phone, a police officer answered. Tan subsequently returned to the scene... and he was identified as one of the assailants in this case by the victim."
Mr Griffiths suffered bruises to his head and left shoulder.
Ng was jailed for a week, as was Thomas Leong Sin Kwang, 37, while their fellow Singaporean Tay Woei Chain, 28, will be spending two days behind bars.
Tan, 34 - a Malaysian -was sentenced to two weeks' jail and a second assault charge for kicking Mrs Griffith was taken into consideration during sentencing.
He was offered bail of $5,000 as he wished to settle his personal matters before serving his sentence.
He must surrender himself to the State Courts on May 14.