Well, blow this! (at the start, anyway)

[Airspeed]

The only key change I noticed was the organist's fingers.
The fireworks racket at the end is so inharmonious, it shouldn't be given a key name.
I do try to understand music. We saw a documentary about a boy with Asberger's.
Apparently, interest in heavy metal is commonly related to mathematical expertise, so I take your point, Nigel.

[nigelb]

Yes Mike, the organist did hit a few keys on the organ, i guess. The modulation that occurs at around 16:36 from C Major to E major is not that inharmonious. Part of the reason it may sound that way is the quality of sound on YouTube. On a good stereo set up, it is not as harsh. Later 20th century composers used far more jarring key changes. C to E major is only a few steps in that circle of fifths. Had he modulated to G Major, the next key on the circle, it would involve only a change of one note in the scale - F to F sharp, whereas E Major has four sharps in it's scale. If you ever want to experience something even more inharmonious (besides some heavy metal) try Schoenberg or Webern. They abandoned the concept of "key" altogether and used the so called twelve tone scale and a technique known as serialism. - OK enough of this. Apologies, because I am probably boring you silly!

Nigel²