In this essay we explore the utility and value of using a theory of change as a programme development tool for signalling necessary programme changes in a project designed to intervene in situations where children are engaged with criminal networks. Whitetown is a real but anonymised urban community in Ireland, where the trial is being undertaken. We discuss co-design of the theory of change with programme staff and the circumstances that required the adaptation of key aspects of functional family therapy, which is a core element of the programme. The experience of applying the treatment modality with fidelity on the ground identified the need to prolong the engagement stage to undertake more intensive therapeutic case management. The theory of change will be further tested by the realities of service delivery in Whitetown's complex environment and relevant lived experience insights from expert workshops will be captured and carefully documented for evaluation purposes.