Part of Man Alone is set in the Waimarino where Mr Shepherd spent a lot of time.
"John Mulgan had relatives living near Raetihi and he often used to go and stay with them," Mr Shepherd said.
However, Mr Shepherd's book is set in Egypt and Greece where Mulgan spent the final two years of his life. He was sent to Egypt in 1942 with the Royal Kents Regiment; and in 1943 he coordinated Greek guerrilla action against the Germans, for which he received the Military Cross.
Mulgan took an overdose of morphine on the eve of Anzac Day in 1945. The reason for his suicide has never been established.
"He was a very troubled man," Mr Shepherd said.
MacLean is Mr Shepherd's first book, although he has had other writings published over the past few decades.
Mulgan is published by Robert Steele, and will be available shortly in bookshops. Recommended retail price is $24.99.