I bought the kindle version and devoured it over three days. Paul Dark is an interesting character, motivated more by self-interest and self-preservation than patriotism. The opening twist is unexpected, setting Dark on a frantic race against powerful enemies. I won't discuss the plot - as other reviewers have done so - but the Nigerian backdrop felt real, and because its an unusual setting (at least to this reader), I was immediately drawn in. In short, very well-researched.
There's a touch of Fredrick Forsyth about Free Agent, but Duns is no derivative of Le Carre and others. Fans of fast paced thrills and intelligent spy fiction will be well rewarded. A great find.