Watch the Oh Daddy, That’s Good! 6 online guitar lesson by Tim Sparks from Post-Modern Fingerstyle Blues
In the solo section, the modal improv is an unlikely mixture of blues and Hungarian Minor. Just in case you're not finding that tricky enough, the improv happens over a descending bass line (D C B Bb A Ab G) fretted by the thumb and syncopated in Biaio rhythm. The next section's harmony alternates between G7 and A7/G.