Purpose – The purpose of this paper is to show the way to unlock the black box of HRM and performance linkages by exploring one of the key variables that mediates the link, namely whether line managers can stimulate improvements in firm performance by eliciting appropriate employee outcomes in a call centre context. Design/methodology/approach – The research draws on Purcell's "People-Performance Model" as a sensitising framework to inform an in-depth case study of a call centre. This provides a mechanism to unlock the HRM-Performance black box by focusing on the ability, motivation and opportunities for line managers to perform and any subsequent impact on employee outcomes. Data were collected over multiple site visits by means of multi-level interviews and a survey of telesales representatives (TSRs). Findings – Research findings indicate that one large client exerted significant control over the HRM policies developed within the call centre. Evidence suggests, however, that line managers'interventions ameliorated some of the negative aspects of work tasks and the HRM imposed by this dependency relationship. Research limitations/implications – This research is an exploratory attempt to better understand HRM-Performance linkages in one specific context. Results are not generalisable across contexts or even within call centres, which can vary extensively. Nonetheless, the research suggests that exploring line management behaviour is a promising avenue for more extensive research. Originality/value – This paper considers HRM-Performance linkages in a service context. Results indicate that both external relations and line managers are critical mediating variables conditioning HRM-Performance linkages, thereby lending support to the notion that hard and soft HRM practices are not necessarily irreconcilable.