When a baby is diagnosed with a condition needing surgery they, and their family, start down an uncertain and unknown path. Living with uncertainty underpins every stage of the journey from hospital to home. These journeys span the highly technical to the mundane. They are likely to involve, at crucial points, medicalised and specialised neonatal and surgical care in paediatric centres of excellence where parents are mere spectators. Yet ultimately parents are able to take their baby home, confident experts in their daily care. Drawing on narrative interviews with 42 UK parents whose baby underwent neonatal surgery, this paper explores how parents navigate this uncertainty through acquiring experiential and lay knowledge and developing expertise in their baby's condition and treatment options. These conditions are rare. Building on sociological understandings of the work of chronic illness, as well as more recent work on newborn screening, sharing information online and examinations of experiential knowledge, we explore lay knowledge and expertise as it intersects with biomedical and surgical frontiers. We demonstrate how the development of expertise is an emergent, three-stage process supported by both biomedical and lay knowledge and elucidate this process of knowledge-building as a scaffold through which to manage uncertainty.