I am a great fan of Stephen Hunter and his Swagger/Sniper books. This is a good one and well worth the read. As he has done of late, and unlike many other writers with serial heroes, Hunter continues to age Swagger and incorporate the ups and downs of that into his writing - Swagger is now 71 years old and has decided to take on the task of learning something about his grandfather. So the story layout goes back and forth between present time and a narrative from his grandfather's foray into fighting gangsters (hence the title G-MAN) and with a little early Mafia thrown in for good measure. Interesting narrative of a time past in which law-enforcement procedures were vastly different, of course. There is lots of gun lore in this book which will please gun-savvy people or which can be easily skimmed by for those who are not. Lots of historical characters included, albeit some with poetic license taken for sure. Have fun with this one!