A red-court infected is someone who has been fed a red court vampire's blood in some quantity, but has not yet fed upon a human person. They are essentially half-turned. One who has been infected by the red court finds themselves insatiably hungry and this soon leads them to kill a human and complete their transformation into a full red court vampire.
The Fellowship of St. Giles is a group of red-court infected who seek out others who have recently been turned and attempt to help them stay how they are. They have strategies for keeping the hunger under control, and they fight against the red court menace.
Mark Manners is a red-court infected who has chosen to deal with this trouble in his own way and has declined joining the Fellowship.