"It was like suddenly being part of an amazing movie. Dad had given me snippets of his life as an airman down the years but never the full story."
Walker was just 20 when he was an air gunner and radar operator with 600 Squadron in England.
Initially tasked with defending Britain under the control of RAF Fighter Command, he was part of a night fighter squadron operating from Manston, Kent, and was heralded as one of "The Few".
After the Battle of Britain, he transferred to RAF Bomber Command and retrained on Wellington bombers, before joining 115 Squadron and flying scores of missions over Germany.
Three of the aircraft Walker flew in crash-landed; one inauspiciously, in a field in Nazi-occupied Belgium. There, he was captured, hospitalised and taken prisoner.
But the Kiwi was not one for languishing in POW camps and hospitals.
Hatching a daring plan to escape from prison with other inmates, he scaled the barbed wire fence and enjoyed a brief moment of liberty before being recaptured.
Good fortune followed him throughout the war and he was eventually placed on a list of injured men who were exchanged for German prisoners.
This little-known, history-making exchange took place in Barcelona in October 1943. Thousands of Allied and Axis prisoners were safely returned to their homelands, in the midst of war.
Angela, 50, lives on Auckland's North Shore with her husband and son.
Like her father, she became a top athlete. She represented New Zealand at the Olympic and Commonwealth Games where she won Gold and Bronze medals in gymnastics.
Ian - who had two surviving daughters and two grandkids - was a talented cyclist who narrowly missed out on being selected for the Empire Games.
"When I read Dad's diaries it was very emotional because I realised he could easily have been killed and I would never have existed," she says.
"After the war he lived a fairly subdued life compared to his time as an airman.
"Just over four years ago I started chipping away at turning his diaries into a book. It was all-consuming and almost all of my spare time was dedicated to putting it together."
Angela says she did not expect the book would ever be published and initially wrote it for his family and his grandchildren.
"I'm thrilled Dad's story is out there," she says.
"He may have been a very humble and quiet man but as I later discovered, he was also very deep."