 Over the next three years while Fianna Fáil was in power a dual-leadership role of Fine Gael was taking place.While Richard Mulcahy was the leader of the party, Costello, who had proved his skill as Taoiseach, remained as parliamentary leader of the party.He resumed his practice at the Bar; what is arguably his most celebrated case, the successful defence of "The Leader" against a libel action brought by the poet Patrick Kavanagh, dates from this period.