“…The aim of the ‘Engager’ programme was to develop and evaluate a complex collaborative care intervention for prisoners with common mental health problems that supports their transition into the community and facilitates joined-up working between health and CJS services (Kirkpatrick et al, 2018 ). ‘Engager’ was iteratively developed from a number of sources, including a realist review of the scientific and grey literatures (Pearson et al, 2015 ), a series of focus groups (Owens, Carter, Shenton, Byng, & Quinn, 2018 ), the lived experience of a group of peer researchers (Taylor, Gill, Gibson, Byng, & Quinn, 2018 ), and a realist formative process evaluation (Brand et al, 2019 ) embedded in a pilot trial (Lennox et al, 2017 ). In designing and planning its delivery, we wanted to try and identify key elements of practice and to understand what was, and was not, effective in helping to engage people, maintain their contact and improve their mental health and general wellbeing.…”