This paper presents a case study of an interpreting event in a Danish courtroom setting. The study investigates the interpreter's influence on the interaction as well as factors influencing the behaviour of all the participants involved. The study also investigates what happens when the interpreter's performance is perceived by participants as inadequate in order to achieve the communicative goal of the event. The model of translation culture, in which cooperativeness, loyalty and transparency are key concepts, is used as an explanatory tool. Although the interaction under study, like all courtroom interaction, is determined by the inherent institutional power differential, it is appropriate to describe it in terms of cooperativeness. The conflict regarding the interpreter's non-normative behaviour is negotiated and settled by way of consensus, and the trial is carried through with the same interpreter despite doubt about her competence. The paper concludes by discussing the effect of special contextual conditions on the proceedings, as well as ethical implications.