The Blue Ring — A.J. Quinnell

Creasy, a veteran mercenary, had found solitude on a small, Mediterranean island, far from the violent conflicts of his past profession.

That solitude is broken when he is confronted by Juliet, a thirteen-year-old heroin addict whose life has been almost destroyed by 'The Blue Ring', a powerful, worldwide cartel dealing in drugs, prostitution and the use of Satanism to pursue their ends.

Now Creasy Has a new mission: to hunt down the evil men who trade in death and degradation... and destroy their paymaster, the evil genius at the centre of an international web of corruption.