Using the money from this job, crime boss Paul Clifton (Stanley Baker) builds up a team to hit a Royal Mail train coming south from Glasgow. A meticulous plan is put in place, but there are obstacles: Jack (Clinton Greyn), the driver of the getaway car in the jewellery theft, is identified in an identity parade and arrested (but refuses to name accomplices to police); gang member Robinson (Frank Finlay) has to be broken out of prison; and Inspector George Langdon (James Booth) is hot on the trail of the jewel robbers, and finds out through informers about plans for an even bigger heist.