What is the main conflict in The Wicked Day by Mary Stewart?

Mordred is born in a time of turmoil, when his mother is very powerful and is causing rifts in the kingdom, especially between her half brother Arthur and her new husband King Lot. Lot orders a massacre of all infants in hopes of eliminating a problem between Lot and Arthur, but one child is saved. The child is Mordred, and Morgause, his mother, whisks him off to a poor fishing family on the Orkney Island. Over the years, she provides sustenance to the family on a limited scale, and almost forgets about Mordred until he is eleven and is instrumental in saving one of her other sons, Gawain.