The Sandtoft settlement in Hatfield Level is the best-documented of several refugee communities established on improved wetlands. Described via the resonant language of ‘plantation’, the settlement connects agricultural improvement in England to imperial expansion in the British Atlantic, acting in the service of empire and state while forging transnational Protestant networks. As improvers, the Sandtoft settlers were fastened to the crown’s agenda to produce profit, subdue commoners, and integrate marginal localities into the nation. As Calvinists and cultivators, however, they met with hostility in England: at odds with Archbishop Laud’s repressive efforts to demarcate a distinctively English Protestantism, while facing a violent campaign of expulsion by fen commoners opposing improvement. Interpreting these experiences through the transnational lens of Protestant adversity, the settler community entangled their quest for religious freedoms with their remit as fen improvers. Moving beyond dichotomous arguments about xenophobia in early modern England, this chapter traces how engineered environmental change forged lines of solidarity and separation.