This book is an operational and tactical study of cavalry operations in Northern Virginia from September 1862 to July 1863. It examines in detail John Mosby's first six months as a partisan, within the context of the larger threat to the Union capital posed by Jeb Stuart. Previous studies of Mosby's career are largely based on postwar memoirs. This narrative balances those accounts with previously unpublished official contemporary records left by the Union soldiers assigned to the defense of Washington, D.C. The formation of the Michigan Cavalry Brigade is fully documented, along with the exploits of the brigade in the months before George Custer took command. Largely forgotten events, such as Jeb Stuart's Christmas Raid, the fight at Fairfax Station during Stuart's ride to Gettysburg, as well as the vital role played by Union general Julius Stahel's cavalry division in the critical month of June 1863, are examined at length.