Turncoat

There's a madman loose in the corridors of time! While America fights for its independence against England, a time traveler wages a desperate struggle against his evil twin. The displaced man is named Noel. His duplicate is Leon, an accident in a time stream who has found a place to happen. Leon's plan: assassinate George Washington and change the course of the Revolutionary War. If the plot succeeds, history will be as warped as Leon's mind. Now it's up to Noel to defeat the British army, and his own worst enemy - himself... (from the back cover of the Ace Books first edition)