I'm now going to ad-lib my long-threatened thread about Mission: Impossible and my single favourite sequence in motion pictures (take that, Red Shoes ballet sequence). Here's the film on the iPlayer right now. The sequence in question is the one in the thumbnail. Of course!

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.