Not that this episode has anything to do with history (which, as we learned in season 1, is of the then, whereas Buffy is very much of the now). If anything, the theme is, adults are fallible too. Also that the sins of the past will always come back to bite you in the end (which of course is what happens when you treat history as if it was of the then and thus nothing to do with you).
Take note (again), Angel. It may not be your mistakes this time, but you can still learn something.
This is also the first episode (I think), where we get our first real example of that good old Whedonverse trope: if things appear to be going well in your relationship, be afraid, I tell you, very afraid.
In fact, this episode hammers home all three themes with a big old sledgehammer, beginning with the very first scene.
That's some serious sins of the past coming back to bite you right there, Mr Old Friend of Giles's.
There's also quite a lot of stressing that Giles is a bit of a fuddy-duddy.
He doesn't like Buffy's work-out music (though, to be fair, Buffy probably wouldn't like it now either. So 1998).
Also, he wears a lot of tweed - a running joke at Giles's expense all through the early part of the episode.
Poor old Giles. It's hopeless trying to exert authority over this lot (even Willow). No wonder he resorts so often to that good old Brit standby; tight-lipped sarcasm.
Never mind. Miss Calendar really does think he's a babe.
And I think she has very good taste.
Handsome and kind and wise, what more could a girl want?
Sadly (though not surprisingly) it was not always so.
Once, the Scoobies learn, to their complete shock, Giles was a punk Sid Vicious lookalike (or else a demon who could decapitate people and then stick its own head on their bodies, as that's Sid Vicious's real, actual body).
Also, far from the spell in The Witch being his first casting, as he claimed, Giles has been dabbling in magic for years.
Often in the company of this loveable old rogue...
...who, this episode makes pretty clear, is also a bit of a masochist.
He gets punched by Buffy...
...kicked by Cordelia...
...and snarled at a lot by Giles. And you sense that he loves every minute of it.
Meanwhile, everyone's illusions about Giles's stuffiness are destroyed for ever.
Evidence.
More evidence.
Also, there's a big old thing where poor Jenny gets possessed by a very nasty demon from Giles's shady past called Eyghon.
Buffy gets a tattoo.
(Don't ask, especially if you're Joyce).
Then Angel saves the day by re-enacting that scene from the original Ghostbusters movie, where Sigourney Weaver, possessed by Zuul the Gatekeeper, smoulders at Bill Murray, "Come into me," and he says, "I think there are two of you in there already."
I think this is the come into me part.
Yep. Definitely at least two of them in there already, and Eyghon makes three.
Actually, I think Angel is too busy saving the day to learn any lessons from all this, so we'll let him off this time.
Anyway, Ethan (inevitably) escapes, Jenny (also inevitably after her horrible experience, courtesy of Giles's dark past) wants a break from Giles.
Silly them. They should never have kissed where Joss could see them.
Then Buffy and Giles share a bittersweet moment of bonding before getting back to what counts as normal for them...
...during which Giles proves that his tight-lipped sarcasm powers are alive and well by pretending to like the Bay City Rollers.
Yeah, right, Ripper.
Other stuff:
Well, Cordelia wins the Miss Self-Centred Sunnydale Award again,
which is okay, because it causes Buffy and Jenny to make these adorable faces.
.
Despite that, and despite herself, Cordelia seems to have elected herself a permanent member of the gang.
She's even (sometimes under protest) quite helpful. Also, her slanging matches with Xander reach a new level of snark, if that's even possible.
Best line: GILES
Is everyone all right?
CORDELIA
Super. I kicked a guy.
Thoughts, anyone?