The Coming of the Terraphiles
Michael Moorcock
 In order to avert the impending collapse of the Multiverse from the mysterious "dark tides" that have begun to appear, the Doctor and Amy join the Terraphiles, a group of humans in the far future obsessed with recreating Earth's distant past and reenacting medieval Earth sports (or rather, unknowingly comic misinterpretations of the same). The Doctor and his new friends compete in a Grand Tournament in the Miggea star system, which lies on the border of parallel realities. The prize of the contest is an ancient artefact called the Arrow of Law, sought also by the Doctor's old foe Captain Cornelius and his crew of space pirates.