The great feud between the clans Campbell and MacDonald in the early seventeenth century AD was part of a power struggle for control of Islay, the seat of the Lord of the Isles, and encompassed wider political, economic and religious change in the region and beyond from the sixteenth century. The discovery of a seal matrix found during excavations at Dunyvaig Castle reveals the personal story of Sir John Campbell of Cawdor (1576–1642) in these broader political events.