The singer, a man in ragged clothing, first identifies himself as "Jimmy Walsh", a ballad singer who only wants to sell some songs to sailors landing at the wharf.  By the end of the story, he reveals himself to be an escaped political criminal, an Irish rebel whose face is displayed on wanted posters and who is the object of an intense manhunt being conducted by the English government.  The irony of the story is that through the bulk of the narrative, the singer is speaking with a Sergeant who is involved in the search but does not recognize that the ragged man with whom he is conversing is the fugitive.  By the end of the story, the singer has brought the Sergeant to recognize unacknowledged Irish sympathies within himself, so when the rebel reveals whom he really is, the Sergeant allows him to escape.