In the early 1930s, many British politicians, journalists, and scientists were greatly alarmed by the feral exploits of a recently introduced North American furbearer that readily escaped confinement. The uncontainable muskrat precipitated Britain’s first legislation to combat non-native invasive species (NIS), triggering a campaign of extermination that was successful within five years, representing a rare instance of mission accomplished in the global history of efforts to eliminate NIS. The short, but intensive, British chapter in the muskrat’s history has attracted just one historian to date. Thirty years ago, John Sheail foregrounded alarm-raising scientists’ efforts to engender political action and provided a detailed account of the Destructive Imported Animals Act’s passage and provisions. Yet many questions remain. How do we explain the acute level of anxiety over the muskrat? How do we account for the surprising ease with which the species was wiped out? And why was there such a spectacular difference between projected and actual numbers at large? These matters will all be touched on, but the novel vantage point adopted is that of the frontier, as understood in the United States and Europe. This requires a broader geographical context than Sheail’s, embracing the muskrat’s homeland and continental Europe as well as a wider source base that extends beyond government records to embrace parliamentary debates, press coverage, and the reports of Bavarian experts that the British government recruited. This approach, the wider spatial setting, and these additional records drive the argument that the muskrat found a new frontier in Britain, where it operated as an unusual kind of creature of empire.