This article considers the larger material and political contexts of the 1636 murder of John Oldham aboard his boat by Narragansett-allied Indians, an event that was one of the causes of the 1636–38 Pequot War. Oldham’s slaying illustrates how the contested region between New England and New Netherland was a “saltwater frontier” where the primary arena of cross-cultural exchange was the coastline and its nearshore waters, not the land. Natives and colonists relied on each other’s maritime technologies and knowledge. At the same time the tricky logistics of their encounters made this zone uniquely perilous. Oldham’s Indian killers were also motivated by an intense trade rivalry between Native powers. A series of events caused them to harbor suspicions of Oldham and inspired them to commit small-scale piracy during his murder. The article concludes that the ensuing Pequot War should be seen as a naval war that turned into terrestrial war, reflecting the English desire to shift the frontier off the water and onto dry land.