At the beginning of 1939, MacBride was at a crossroads. The disfiguring fallout of the feud with Seán Russell, a feud in which MacBride was significantly invested, had led to the departure of most of the IRA ‘old guard’ during the heated 1938 Army Convention. MacBride had officially ended his active membership of the IRA, the organisation through which he had defined his personal and political sense of self for two decades. In many respects, it was an opportune time to sever links with the IRA which, under Russell's stewardship, had embarked on a dangerous new strategy designed to satisfy the militants who had long grown impatient with ‘political’ intrigues. The first step in this programme was the transfer in December 1938 of legitimate republican authority from the ghostly remnants of the Second Dáil to the Army Council of the IRA. This was closely followed, on 12 January 1939, by an ultimatum addressed to the British Foreign Secretary, Lord Halifax, demanding ‘the withdrawal of all British armed forces stationed in Ireland. When the deadline passed – apparently to the general disinterest of the British authorities – the scheme known as ‘S-Plan’ (or Sabotage Plan) was implemented.

This was the brainchild of James O'Donovan, the former Director of Chemicals for the IRA, now an engineer for the Electricity Supply Board and married to Monty Barry.