Using multiple case studies of health and justice services to inform the development of a new complex intervention for prison-leavers with common mental health problems (Engager).

The multiple case study design contributed insights as to how health and justice services work together. The main themes identified are well known factors in health and justice co-working. However, the novel insights were gleaned examining interdependence and interactions in complex, multifactorial phenomena and practice, in particular the importance of shared practice and supervision models. The approach of selecting a small number of cases representing identified knowledge gaps contributed a valuable addition to the program theory and delivery for an innovative complex intervention.