Brereton's book made up of letters comes out of the English Civil War (1642-1646). A Parliamentary general, Sir William was engaged in the siege of Dudley Castle, Bridgnorth Castle and the fortifield cathedral close at Lichfield. The letter book contains copies of letters sent and received by Brereton. There are details of his victory against the last Royalist army in the field, his various sieges, his constant need for money and troops, and the movements of King Charles I prior to his surrender to the Scots. The Introduction details a history of the civil war, of the battles and skirmishes, up to the writing of the Letter Book. A conclusion relates what happened after: the end of the war, the trial and execution of Charles I, the Interregnum and finally the Restoration and Brereton's retirement from public life.