Relationships are central to therapeutic community treatments and the process of change that is facilitated. In this paper, we present a systematic critical case study of a service user who undertook a course of treatment at a now closed therapeutic community day service in south London. Using the contents of electronic patient notes, outcome measures, review letters, staff reflections, and a post-treatment interview, we show the importance of relationships within TC care. While literature regarding the efficacy of TCs does exist, there is less research concerning in-depth case studies of treatment. The importance of relationships within the TC model has been theoretically explored but not clinically demonstrated in the literature. Our case study supports findings from a recent RCT concerning TC care versus ‘treatment as usual’ for borderline personality disorder. Our research further supports an approach emphasising the importance of relationships to TC work with personality disorder beyond any specific therapeutic modality.