He volunteered to pose as a mature student making a documentary about voluntary work so that he could meet the residents of one of the poorest areas of Britain's poorest city - Possil Park in Glasgow.
Having arrived in Possil Park - a place where "you only want to live if you were born there", according to his taxi-driver - he was unsure about whether he had made the right decision.
"This is something out of East Berlin," he said despairingly as he surveyed the derelict, graffiti-strewn buildings for the first time. Actually, I visited Soviet-era East Berlin before the wall came down, and in comparison East Berlin looked like Knightsbridge.
As Leslau settled into his flat (air-conditioned thanks to a missing window pane), he pondered life on an £8.50-per-day Jobseeker's Allowance.
Next day he was out meeting the good folk of Possil Park. His first stop was the Milton Disability Forum, where Ronnie, who ran the drop-in centre despite being disabled herself, provided essential services for the area's needy. Nick was unfazed as he got down to cleaning the toilets. "There is," he said, "something therapeutic about doing something really useful."
His next engagement was at a riding school for the disabled. Here, he met Lynn, who performed miracles keeping the school open. She revealed that they had no money for tables in the café so they had made their own with donated wood.
Leslau also visited some of Possil's most deprived folk as part of a befriending service. These included Alan, who had become blind as an adult and was clearly yet to come to terms with his condition, and Marion, a housebound pensioner who lived in pitiful squalor.
The experience was having an immense effect on Leslau, who confessed that the conditions under which his new neighbours lived made him feel slightly "repulsed" about his London opulence. His genuine warmth and caring nature was clearly endearing him to them as well. If the property-developing ever dries up, he would make a fantastic care worker on the basis of this film.
The came the time to divvy out the money. Leslau wrestled hard with his conscience before shelling out a mind-blowing £340,000, to Lynn at the stables, Ronnie at the Forum and Andrew (a donation to a guide dogs' charity and five years worth of Rangers seasons tickets).
Even when you know your emotions are being manipulated, it is sometimes hard not to shed a tear. And in this case, there were real people living real lives benefiting to the tune of thousands.
In fact, say what you like about the artificiality of The Secret Millionaire, it is one of the few programmes which changes people's lives for the better.
More millionaires should try it.
