Like a Hole in the Head by James Hadley Chase
Ex-army musketry trainer, Jay Benson and his wife Lucy's dream of running a shooting school turns sour as the school heads towards certain closure. They need money - quickly, and a lot of it. At the eleventh hour Augusto Savanto, head of a vast corporation in Venezuela, walks into their lives with a proposition they can scarcely refuse - he will pay them $50,000 to turn his son into an expert marksman, in nine days. Desperate for money they accept the challenge but find themselves in a deadly game of ruthless vendettas and vengeful murder.