Denis grew up in Dagenham, Essex, in a small two-bedroom house managed by the local council. At fifteen he left school to become a printer's apprentice, but within a week he fled the print shop for a magic shop. At age eighteen, he became one of the youngest members of the Magic Circle, and on his 21st birthday he was on a Greyhound bus heading for his first magician's convention in Philadelphia. As a magician and magic dealer, Denis had an opportunity to tour the United States quite extensvely. He loved the place and people so much he couldn't wait to go back.

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Denis hankered to conjure something different. Encouraged by his mentor, American movie director Cy Endfield, he left the magic game to become a writer of scripts and songs, and a dabbler in album production. Notably, one of his songs ended up on the Benny Hill Show. In 1979 Denis decided to write a play, A Moment of Life, which was showcased by the Royal Shakespeare Company in Stratford upon Avon. He was then invited to join the company's writer's workshop. Despite his early successes, the search for a "proper job" remained elusive in London, and Denis took a chance and moved to the States. Within two years he was senior writer at a major advertising agency and writing plays for the Washington Theatre Festival. In the early nineties, with American wife Frances Erlebacher, he started his own agency, The Creative Shop, while continuing to moonlight as an occasional playwright.

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Encouraged by Frances to take a break from plays and write up the family's adventures during their annual visits across the pond, Denis wrote A Yank Back to England: The Prodigal Tourist Returns, his first book.Shortly after it was published, Denis decided to write a book for his teenage daughter, Kate. Research took him to Jerusalem, The West Bank, the Negev desert, a firing range in Maryland, even a magic shop in Washington DC. After some nail-biting writing years, that story finally became Striking Terror.