As well as neighbourly affection, his children had always been fascinated by Mr Mills' daily bread run.
"Roger leaves very early in the morning and there's a real fascination - where does he go in his truck, where does he get all the bread and what does he do with it all?"
The answer is: he checks in with Martinborough stores about 8pm at night to see what they need the next day, gets up in the wee hours to pick it up from Masterton and then delivers it to Martinborough stores in a 23-year-old white truck.
Mr Mills has been doing it for 58 years - Mr Percy's mother remembers his runs from her time growing up in Pirinoa.
He started off working in his father's bakery, delivering to Pirinoa and Kahutara in a Morris Minor.
He has been working for Breadcraft for the last 40 years.
The Old White Truck was published after a draft was read out at Kay's 70th birthday party - and, after about 50 people pre-ordered the book, Mr Percy was forced to publish it.
"I floated the idea of changing their names, but they're so iconic in Martinborough, people would have clicked anyway."
Mr and Mrs Mills said introducing yourself to neighbours was an "old-time thing" but alive and well in Martinborough.
The three of them agree that Martinborough has something special - lost dogs and keys are returned promptly, there are often offerings of honey and scones, but it could be about any small town in New Zealand.
"Everybody is very proud of their town and little places," said Mr Percy.
"There are people in each little town who do similar sorts of things, and that's important to protect and support."
It is Mr Percy's first published children's book, but other Martinborough stories were in the pipeline, including another instalment of Mr and Mrs Mills' adventures.
Mr Percy said that thanks to some enthusiastic salespeople at local stores, he had sold about 200 copies of the book and, thanks to relatives, the books have ended up as far away as Saudi Arabia and the United States.
The book is available at Martinborough cafes, online at www.martinboroughstories.co.nz, and will shortly be available at Hedleys Books.