Our protagonist, Nick Fury, gets out of his helicopter, along with his sidekick Agent Maria Hill, and exchanges some rapid-fire dialogue with Agent Coulson as he heads down, down, down into the depths of the installation. He’s arrived in a helicopter, a symbol of power, and now he descends deep, deep underground. What does he talk about with Coulson? “A bunch of stuff.” The Tesseract, we come to understand, has done something surprising, which has necessitated the evacuation of the installation. The Tesseract, which, again, we don’t know what it is or what it does, is kept deep, deep underground because it’s so freaking powerful.
(Incidentally, why must the installation be evacuated? The answer: because The Avengers, in order to make the ton of money it needs to make, must be rated PG-13. The installation is about to go sky-high, so to speak, and if the movie begins with a catastrophic loss of life, it becomes Saving Private Ryan instead of the colorful spectacle it needs to be.)