This essay takes as its starting point the resemblance between the historical practice of diplomatic representation and the rhetorical practice of metonymy. The early modern ambassador acted as a substitute abroad for the sovereign who sent him and metonymy describes a comparable replacement – in words – of one thing by another associated thing. Yet metonyms can all too easily become confused with their referents or even come to replace them, as the sign is taken too literally for its signified, creating a kind of rivalry between representative and represented, as competing sources of authority, in a shift from relations of likeness to opposition. As 3 Henry VI points out – and as this essay argues – the metonymic characteristics of early modern ambassadorial representation made it vulnerable to this drift towards antithesis. Antithesis, the figure of opposition, governs the contentious disorder of 3 Henry VI, from the rhetorical patterning of its speeches to its structure and subject matter and politics. The Earl of Warwick’s embassy in Act 3 is no exception: it is the pivotal point around which the play’s oppositions turn. As Warwick moves from representing to replacing Edward IV, the figures that express his migration from substitution to subversion reflect on a comparable instability in European diplomatic culture. Diplomats could easily misrepresent.