Q: hey bill what key is the song Help! by the beatles in? Sounds like Amaj but it has a G chord in it and that isn't in Amaj. If it is A major, where does that G come from?
A: i would say the intro is Bmin, setting up to seem like it's going to be in D, (hanging on the final A7 sounds like we're about to go to verse in D) but surprise, it's just not. verse is in A. this coasts along comfortably and normally in A, for a while. Then, when it goes "help me if you can i'm feeling down" this is essentually 2 parallel universes running side by side. according to what came before, this sounds like the 2 min chord. so the G will now sound like an interesting flat7. but by the time we hit the E7, all of a sudden you can re-map the entire last 4 bars (two chords worth) as if they have been in Bmin (D) the whole time. similarly showing up at that A7 hang about to put you to bed in D, which again it does not, it just stays in A. just does. to have the fun of going around and doing it all again