Midwife Sylvie Marren has delivered over 1,400 babies in Harbor Springs, Michigan. Then she delivers one with a perfect crescent mark on her shoulder blade - and realizes every baby born since March carries the identical mark. Her investigation runs through a pregnancy app and free "personalized" prenatal vitamins to Halcyon Bio's Crescent-9: a germline-editing vector that boosts immunity, dampens defiance, and brands a generation.