Cowley, who was approached by long-time museum committee member Pat Flynn with the book idea, said she felt excited to write the story, but also felt challenged by the prospect.
"How could I create an interesting story about fell engines on the Rimutaka Incline?' said Cowley, who made several visits to the museum to do her research.
"But the old adage 'the life is in the detail' holds true. I decided to focus on one engine and one journey.
"Although I made up the story, it wasn't fiction. The Rimutaka Incline was infamous in bad weather, and rail carriages had been lost in a storm."
After more than 70 years of chugging up the notorious Incline, the fell engines became obsolete when the Rimutaka Tunnel was built in 1955.
H199 was then gifted to the town of Featherston, and mounted on a plinth in a children's playground, where it began to deteriorate until it was restored by the Friends of the Fell Society.
For Cowley, H199 is heroic not only for its uphill treks, but because it is a survivor.
"It's the only one left. All the other [fell engines] were broken down for scrap metal," she said.
"H199 could have suffered the same fate. For years, it was outdoors, in a children's play area, and it had deteriorated considerably. That engine is a hero in its own right."
Hero of the Hill is written in a traditional poetic ballad style - which Cowley describes as "clicketty-clack" rhyme - to mirror the rhythm of a train on the tracks.
Wellington-based artist Philip Webb, who has worked with Cowley on several projects, provided the simple, yet expressive and colourful illustrations.
"Philip is meticulous with detail and has a lot of energy in his work," said Cowley.
"I told Scholastic I thought Philip was the only illustrator for this book and, fortunately, they agreed."
The launch for Hero of the Hill will take place in Featherston on Saturday and will feature a speech from South Wairarapa Mayor Adrienne Staples and a performance by pupils from St Teresa's School.
Cowley is looking forward to the launch, but is also looking forward to spending her free time doing some woodturning now all her writing projects for the year are done.
"My lovely husband, Terry, buys me tools for my birthdays and only rarely complains about wood shavings in the bed," she said.
The launch will take place Featherston's Anzac Hall at 2pm on Saturday, September 28. For more information, contact the Fell Locomotive Museum on 06 308 9379, or at fell.loco.museum@xtra.co.nz.
