The Fear Merchant — Ramsay Thorne

Everyone wants to lay hands on Captain Gringo in Nicaragua! In this revolution-wracked land where the man with guns is king and those who grovel before him conspire behind his back, no one can be trusted. But ruler and rebel alike want the guns Captain Gringo's running - if only to keep the other side from getting them.
With his eyes wide open and his Maxim at the ready the Captain is primed for action: in the bed of a Chinese girl whose eyes are startling grey at the challenge of a general who has only one eye, at the silent command to murder in the cold gaze of a high-born lady, at the demand for love in the hot, savage stare of an Indian girl. For no one can fight and no one can love like Captain Gringo.