Duns writes spy fiction featuring an MI6 agent called Paul Dark, set during the Cold War. Duns's novels are influenced by Fleming,Len Deighton and John le Carré; his debut novel, Free Agent (2009), was one of the Telegraphs "thrillers of the year" in 2009. The BBC optioned the television rights to the Paul Dark series in 2009, although Duns' own website notes that the option has since lapsed.
In 2011, he praised debut spy novel Assassin of Secrets by Q.R. Markham, but after reading allegations that a scene in the novel was plagiarised, Duns investigated further and discovered that large sections of the novel had been plagiarised. He informed the British publisher, Hodder, and the book was pulled by Hodder and US publisher Little, Brown and Company.
In 2012, he discovered that novelist R. J. Ellory had written positive reviews of his own books while responding negatively to rivals, on the Amazon website, via the use of sock puppets. Ellory admitted he had done this, and apologised for it. Duns has also examined methods used by British author Stephen Leather since his admission in 2012 that he uses a network of sockpuppets to promote his own work online. Duns has also alleged that Leather has harassed him online in retaliation.
In 2012 Duns helped organise an open letter signed by over 50 authors condemning the use by certain authors of sockpuppets, fake reviews and other deceptive marketing techniques.
^Duns, Jeremy (7 March 2010). "Ian Fleming's book about gem smuggling in South Africa is as thrilling as Bond, and should have been a blockbuster film starring Steve McQueen. So what went wrong?". The Sunday Times. London. pp. 4-5.