The Day Of The Boomer Dukes — Frederik Pohl

A delightful time travel romp. What happens when a bored criminal from the future returns to a more exciting time in the past? Foraminifera 9-Hart Bailey's Beam is about to find out. He's gathered a cache of high-tech weapons to take back in time with him, with the intention of teaming up with the legendary New York Mafia. Upon arriving in our time he meets a street gang named The Boomer Dukes and he asks them to "take me to your Mafia." From there nothing goes as planned.