The story of the poem is broadly thus: The king of Scotland needs to fetch the daughter of the king of Norway from over the sea, and therefore needs a very good sailor to go and get her. It is understood that this is a bad time of year for sailing (probably winter), and therefore the choice of captain ("skipper") of the ship would be put in considerable danger. Some "eldern knight" at the Scottish court -- he is not named, specifically -- suggests the excellent sailor, Sir Patrick Spens.