Unscheduled and urgent healthcare represents the largest area of activity and cost for the UK's National Health Service (NHS). Like typical complex systems unplanned care has the features of interdependence and it has structures at different scales that require modelling at different levels of detail. The aim of this paper is to discuss the development of a multifaceted approach to study and optimise this complex system. We aim to integrate four different methodologies to gain a better understanding of the nature of the system and to develop ways to enhance its performance. These methodologies are: a) lean/flow theory to look at the process and patients and other flows; b) simulation/system dynamics to undertake analytical analysis and multi-level modelling; c) stakeholder consultation and use of system thinking to analyse the system and identify options, barriers and good practice; d) visual analytic modelling to facilitate effective decision making in this complex environment. Of particular concern are the boundary issues i.e. how changes in unplanned care will impact on the adjacent facilities and ultimately on the whole healthcare system.