The sequence really begins with a choreographed bit of sitting-on-a-train, wherein Ethan Hunt gives a broad sketch of his plan. Essentially he says "We all have jobs to do" but what those jobs are is basically secret. Heist movies can go both ways. This one hangs on surprise.
The heist target is an IMF mainframe - they're going rogue and infiltrating their own agency. It's crucial to what the scene, and film, means at the most basic level. The institution is corrupt, our 'heroes' are pitted against it. Lots of the film is foggy but *this* is clear.
The remainder of the early train scene has one major purpose: to tell us the mission is impossible. This sequence delivers on the basic promise of the film (the whole series, arguably). The impossibility of the mission is exciting for the crew, compounding audience excitement.
Though this scene doesn't tell us what Hunt's solution is, it's crucial that it lays out the problem in a very clearly readable way. The vault's high security is hammered home. We're shown *and* told at the same time.
In a way, it's like being presented with all of the evidence in a murder mystery - the things we remember later when the crime is solved so the resolution is satisfying. At the same time, it's more raising of the stakes. Every locked door is another puzzle that needs solving.
Some of the problems seem like total red herrings - the key code on the door, the retinal scan - because Hunt and co. are going to bypass them entirely rather than take them head-on. But they have another use later...
What an eccentric keypad, by the way. Numbers and... well, why not just letters? As Donloe only uses the numbers maybe the symbols have another specific use. Nothing ever comes of them - maybe it's something to revisit and twist in Mission: Impossible 7 and 8.
When we first see the 'black vault' it's nothing of the sort. It's an interesting design - divergent from the description in the shooting script (the one credited to Robert Towne). Oh - and note the clock on the wall. It's 10:00 right now.
In the script, "the glass and tile walls of the room overlook computer storage towers." On the screen, the walls themselves seem to be computers. The production design feels like the room is "inside" the data, that getting in here is getting to the centre of things.
Now some rules that ARE directly important: three systems operating whenever the the technician is out of the room. Again, De Palma *shows* us what he can while we're also being told.
Cutting back to "Oh crap" reaction shots is a simple, effective bit of stakes-raising.
The room changes dramatically when the Intrusion Countermeasures are active/not active. Why? Well, it's for our good, really. The change is very plainly established during another bit of show and tell.
(You'll see the time tick over to 10:01 in the same shot, in fact - time pressure becomes a thing later on)
Now we come to the most interesting element of the whole scene. The iced tea.
That's a heck of a place to put your tea, isn't it, Mr Donloe? It's almost as if he wants it to fall on the floor. A cheeky bit of cheating to make the next bit work - showing us that the security system works and what that looks like.
The 'red for danger' colouring is pretty straightforward. I think there's a little more going on. I think this sequence adds up to a war against the body. Against the rubbishness of biology. Against human imperfection. So, the tea is organic and wet in a crisp, dry machine world.
So far, all of this has been established in a scene without score, with emphatic, 'signposting' sound effects in a tense silence. What a perfect mood to explode with the exciting Mission: Impossible theme - and what a way to say "We're off an running." Music and sirens blaring!
The first portion of the heist is the infiltration of the Langley campus, done with good ol' disguises and IMF maskcraft. We had no idea at all this was coming, but it's well-told and exciting to watch unfolding. The dialogue is as urgent and active as the camera.
We've learned all about the videofeed spy glasses earlier. Reprising them now works well in a "rule of three" sense, bolstering a crucial late sequence in the film, but they're also put to good use right now, to quickly and simply show us the alarm hack unfold.
I could single out tiny, elegant details all day. Even simple choices like the hand on the shoulder here, pre-empting/motivating the camera move, are cinematic, clear ideas.
