All verses start with this riff (repeated twice):
Then the first verse goes (repeat twice):
This is like A, A, and a variation on E-minor, I think.
The 2nd and 3rd verses start with the main riff, but instead of
going right to the A, A, etc. it first goes through these licks:
Before the 2nd verse goes to the 3rd (and the 3rd to the fade out),
The fourth verse begins the same way as the other three and fades out
repeating the A