He said three things helped trigger the book, which took him 18 months to craft.
The first is that he used to work for a television times magazine which took him to the Fall's Rd, Belfast, in 1970, where tanks and barricades were at either end.
"It was quite an evil thing to put into a residential street.
The memories provided the inspiration for the opening sequence in his book.
Secondly, McGill's Irish diaries were "invaluable because I travelled around all of Ireland at that time".
And thirdly, viewing photos during his time in Ireland triggered memories and "really buoyed me".
One of David McGill's many interactions during his travels in Ireland.
McGill was pleased with the final book in the series.
"I've not been happy with all my books but I am with this one.
"I probably put a bit more into it in terms of thinking about it, rewriting it, and it is also quite personal as I'm also looking for my own ancestors which I haven't found.
"This is the most absorbing book I've done for a while, and also the most vexing, I suppose."
McGill, 79, who has about 60 non-fiction and fiction books to his name, doesn't think he'll write another book.
"This is the biggest bestseller novel this country has ever known. It is being made into a film. It's about the coal mining era of the West Coast."
Despite the challenges, McGill has enjoyed his book writing career.
"I've always regarded it as continuing the journalism.
"You get into the habit of writing, in journalism, and you just keep ticking over really.
"I was talking to playwright Roger Hall, who I used to flat with, and we both agreed that we could have written more if the market would allow it but they don't."
To purchase a copy of Back Home In Derry and other titles go to www.davidmcgill.co.nz
The shaky 1995 ceasefire between Republicans and Loyalists proves the best and worst of times for ex-policeman and ex-national security operative Dan Delaney and his family to track down Irish ancestors. Instead of finding his grandfather's origins in County Cork, he finds his own troubles with car theft and a clumsy horse but likes the Clonakilty black pudding and an IRA song about Derry. The trouble ramps up in Dublin, where his daughter is almost killed in a grenade attack outside the Abbey Theatre. In Belfast he is caught up in violent clashes between marching Protestants and protesting Catholics. His mother's wrong-side-of-the-blanket relations in Derry have left him disinheritance hassles and an old foe who intends to make them terminal. In the final outing for Delaney, Republican and Loyalist enmities are the historical backdrop, but again he must rely on the ad hoc Kiwi approach to problem-solving that ensured his family survived security threats in Sydney, Israel, his native West Auckland and Wellington. His long and modestly undistinguished career reaches a final solution to both his origins and his family's survival. It is a win/lose scenario - and the loser dies.
