Shadow Chasers by Paul Adam

Rob Sullivan, a British customs officer, is on secondment to Brussels where a tiny unit from the EU's member states are supposed to tackle all excise duty crime in Europe. Alone in a dreary city, Rob finds much of his work either boring or frustrating, but occasionally a big fish ripples the surface of their pond. This time he and his collegues, including the intriguing Claire Colmar, link two cigarette smuggling operations. While they are pretty sure they can name some of the players they need to prove it, and they want to track back to the real mastermind behind the scheme, but every time a lead appears they reach the witness just after they've met an 'accident'. Increasingly desperate they begin to take short cuts, with terrifying consequences.