The town of Lichfield is celebrating Festival week. The highlight of this year's Festival is a reconstruction of the siege of the cathedral by Parliamentarian troops during the Civil War. The police have big problems: assassination threats have been issued against the guest of honour, Polish Premier Kosminski, reputed to be descended from Jack the Ripper; the priceless Lichfield Gospels are under threat of vandalism and theft; and they receive a tip off that the…