This is an Ian Martin/Lloyd Battista (good guys) Nat Polin/Earl Hammond (bad guys) collaboration that I heard a rerun of back in my original listening days. It's based on the old Pinkerton security/detective agency (now known as Securitas today..."The Securitas method" might have had a ring to it too, I suppose). This is sort of a precursor to today's TV detective shows in that there are a couple of plots going on in the same episode. This one was handled in a sort of "doughnut" fashion...The story starts with Martin and Battista investigating the (apparently true, as E.G. said this was based on Pinkerton case files) Rock Island train robbery near Morris, IL. where a railway employee was killed. They then leave the investigation there temporarily to deal with another robbery in Tennessee. Afterward, they return back to the Morris investigation. Worth a listen...I like all the actors involved (Martin and Battista were fun to listen to together as the Pinkertons) and James Agate, Jr. did a good job of adapting the case files.