This paper presents a theory of dual prominence in tone mapping. Evidence is drawn from tone movement observed in the Chinese Zhenhai dialect. Two prominent positions are found to be implicated in determining the surface sandhi forms: prosodic edge and metrical head. In Zhenhai, the initial tone is preserved and moves to the stressed final syllable in the output, giving rise to tone movement. An Optimality-Theoretic analysis of tone movement is proposed in which both prominent positions are referred to by positional faithfulness and positional markedness constraints, whose interaction yields diverse surface sandhi patterns. The theory makes possible a richer typology of tone-prominence interaction.