This paper seeks to present findings from a longitudinal action research study aimed at exploring one such innovation. Little is known about the micro-level impact of health service innovations over time. The paper shows that action research is a participatory approach ideally suited to monitoring the process and outcomes of change. Over 20 months, an action researcher studied the work of four interprofessional care co-ordinators (IPCCs), whose role was intended to speed patient through-put within a London teaching hospital general medical directorate. The action researcher kept regular participant observation field notes and supplemented these data with a profile of IPCC patients (n = 407), in-depth interviews (n = 37) and focus groups (n = 16) with staff. Throughout the study, findings were regularly fed back to participants to inform practice developments. The findings in this paper show that, in spite of the original intention for this role to provide clerical support to the multidisciplinary team, over time the role shifted beyond its implementation into practice to take on more complex work from registered nurses. This raised actual and potential governance issues that were not attended to by service managers. A complex and turbulent context disrupted managers' and practitioners' abilities to reflect on and respond to these longer-term role shifts. This paper argues that the complex nature of the innovation and the setting in which it operated account for the role shift and the lack of attention to issues of governance. Current innovation literature suggests that implementation into routine practice represents the end-point of an innovation's journey. These findings suggest that certain innovations may in fact continue to shift in nature even after this "end-point". The conclusions drawn are likely to be of global interest to those interested in complex health service innovations.