Sergeant Crusoe

Luke Sharp is unaware that he has a double - Marco da Silva, the ruthless criminal gang leader known as 'Silver'. When a pair of vigilantes intent on taking their revenge against Silver shoot Luke by mistake, his life is changed dramatically. Convalescing at his grandfather's home, he agrees to transcribe the old man's wartime memoirs of his exploits in the South Pacific. However, Silver finds out about Luke, and attempts to coerce him into work as his double in crime...
Sergeant Crusoe by Leslie Wilkie