Updated punctuation:

    Am                               G Am
  I did not come for naught. I came to warn:
       C               Am                  E7              Am
  MacDougall's men are coming, lads. They'll be here in the morn.
  I travelled hard upon the road, through the rainy night.
  Call the men to arms, my lads. There'll be a heavy fight.
  
  It seems the lass you've taken in is promised to anither.
  She's na wha she appears to be. She lied about her mither.
  She said she was a tinker's lass who lost her way saw blind,
  And so she came unto your door. She knew you'd treat her kind.
  
  I fear she has deceived your will, and know you would believe her.
  The clothes upon her face and hands, you'll know she's no a tinker.
  For though her cloak is ragged now, her skin is soft and pretty.
  She's traded her fine linen in for garments torn and dirty.
  
  I see she has won your head, and you'll give her freely,
  But for the kindly deed you've done, I fear you'll pay most dearly.
  MacDougall's men for vengeance come. Their minds are bent on slaughter.
  For hear me weel, she's no' a lass, she is MacDougall's daughter!

(Transcribed by me based on recording. Dialect may be inauthentical. Song origins unknown.)