Doctor Who: The Myth Makers — Donald Cotton

Long, long ago on the great plains of Asia Minor, two mighty armies faced each other in mortal combat. The armies were the Greeks and the Trojans, and the prize they were fighting for was Helen, the most beautiful woman in the world. To the Greeks it seemed that the city of Troy was impregnable -- only a miracle could bring them success. Help comes to them in a most mysterious way, as a strange blue box materializes close to their camp, bringing with it the Doctor, Steven, and Vicki, who soon find themselves caught up in the irreversible tide of history and legend.