<P> Catherine Douglas, later Catherine "Kate" Barlass, was a historical figure who tried to prevent the assassination of King James I of Scotland on 20 February 1437 . She was a lady - in - waiting to Queen of Scotland, Joan Beaufort . </P> <P> She was a member of the powerful Clan Douglas . Her mother was a daughter of David Lindsay, 1st Earl of Crawford and his wife Elizabeth Stewart daughter of Robert II, making her a first cousin once removed of the King . </P> <P> Legend has it that during the King's stay at a Dominican chapter house in Perth, a group of men led by Sir Robert Graham came to the door searching for the King in order to kill him . The King's Chamberlain, Robert Stewart, Master of Atholl, had removed the bolt from the door of the room in which James and his queen were staying . </P>

Where does the expression katie bar the door come from