Born in 1861 in Yorkshire, Mr Smithies was head-hunted and brought to Wanganui from Petone by the mayor of Wanganui, Alexander Hatrick, in the early 1900s. Mr Smithies was a talented engineer who was head of the gasworks, and also became the town clerk. He was the head of the Masonic Lodge and was a society leader.
The scandal began in 1905 when he disappeared, leaving behind his wife, Bridget, and 10 children.
"It was awful for Bridget.
"She was part of high society, but she had to leave her nice house on St John's Hill and take in work to earn a living for her family. Even though it wasn't her fault, she was terribly snubbed by people," Mrs Couchman said.
Two years later, George Smithies was found in Australia - where he had started another family - and brought back to Wanganui to face a desertion charge. The court case was further scandal and something of a farce: Mr Smithies' lawyer was another Wanganui mayor, Charles Mackay, who was also acting for Bridget Smithies.
George Smithies escaped conviction on the desertion charge and immediately fled for the United States where, according to Mrs Couchman, his tale became murky and mysterious.
"I've done so much research, but I cannot find out where or when he died. The last positive identification of him was in Alabama when he was in his 70s."
Mrs Couchman said George Smithies' descendants are spread far and wide. His oldest son lived in Invercargill and had 10 children himself, and many of his descendants still lived in Southland. There are also relatives living in Wanganui.
"He actually left good families behind. A lot of the Smithies are engineers, which is something they obviously inherited from George."
During her research Mrs Couchman had encountered resistance from some descendants, who did not wish to have the family's dirty laundry aired.
There are few photos of Mr Smithies remaining because many of them were ripped up or burned by disgruntled relatives.
And what does Mrs Couchman think her erring grandfather would say about her book?
"I'm quite sure he'd think I was the cheeky little granddaughter who exposed his family," she said with a laugh.
Doreen Couchman is selling her book, Restless Engineer, for $35 including postage. To order one, contact her at doreencnz@yahoo.com.