It doesn't seem to be diatonic. There are many ways to look at it, but I'd probably say for the verse the first to chords in C major (A minor) then it modulates to E major. For the chorus same thing; Dm and C in C major, B and E in E major.

Could be a bit tough for a lead if its at a fast tempo, you could just look at each chord on its own and play chord tones.