Leather's novels frequently include themes of crime, imprisonment, military service, and terrorism. Settings are typically London and the Far East. Leather writes different series in slightly different genres. The main character of one series, Dan 'Spider' Shepherd, is a former Special Air Service soldier who becomes an undercover policeman. Another series, "Jack Nightingale", is about a former police negotiator who becomes a private investigator; this supernatural detective series is also published by Hodder & Stoughton and includes the books "Nightfall", "Midnight", "Nightmare", "Nightshade" and "Lastnight".