Watch the Forgotten Son online guitar lesson by Angus Clark from Hard Rock Survival Guide: Lead
Big sweep at the top is a B dominant 7 b9 chord, starting on the F#. Crazy sounding but it makes a big statement. We're in the B phrygian major (B C D# E F# G A) which is a mode derived from the harmonic minor scale. Then the whole thing modulates up to C#, which I treat as C# phrygian, then D phrygian. Pay close attention to the triple-picking lick, it's a killer. As is the sequence on the D chord.
The band turns around on a B chord before launching back into the main groove which is in E minor. I handle this just by hitting an F# on the B chord and then a unison bend on E for the downbeat of the next section. Here again the bigness of the unison bends is what I'm using to make the solo arc over the business in the rhythm section. Last lick is a descending sequence that I'm just partial to. It's really descending sextuplets, which would be "did-dle-ee did-dle-ee" but the first string in each pattern features a grace note which makes it "did-dle-ee-bum did-dle-ee", so it's go a bit more going on. Watch how I use a three-note-per-string fingering but don't shift positions on the 2 to 3 string crossing, creating a double picked D. That's a hot tip.