An unusual combination of factors meant that Northern Ireland featured prominently in British Conservative thinking during the course of the extended efforts by the UK governments led by Theresa May and Boris Johnson to implement Brexit, following the 2016 referendum. Opposition among Conservative backbenchers to the differential treatment of Northern Ireland under the proposed ‘backstop’ arrangement contributed to the defeat of the Withdrawal Agreement negotiated with the EU by May. However, after Johnson became Prime Minister, a deal involving greater divergence between Great Britain and Northern Ireland secured overwhelming support from these same Conservative MPs. This paper explores the origins of, and influences upon, these debates on Northern Ireland within the parliamentary Conservative Party. Drawing on interviews with decision-makers and advisers, it identifies the lines of thinking that shaped Conservative positions on Northern Ireland after the party returned to government in 2010. It argues that two distinct modes of thinking about Northern Ireland co-exist within the party's collective mind: the notion it constitutes a ‘place apart’ from Great Britain, and the belief it remains integral to the UK. The circumstances of 2018–19 meant Conservative MPs were forced, reluctantly, to choose between the implications of these ultimately incommensurable perspectives.