Draco's got a big project this year, and it has zero to do with school.

No, he hasn't taken up cross-stitch. Keep guessing.

We don't know the full extent of his mystery job until later in the film, but we learn what "Step One" is pretty quickly: Draco is doing something weird with the vanishing cabinet in the Room of Requirement. He visits the cabinet, puts things in it, and sees what happens when he opens and closes it. As you may have guessed from its name, the cabinet makes things disappear.

However, things (re-)appear in the cabinet as well. For example, Draco puts a live bird in the cabinet and vanishes it, but it does come back later. Dead.

Yeah, er, we know…not a good sign. It seems that Draco is sending/receiving things via the cabinet…and it's quite possible the person or people on the other end are up to no good.

Why does this matter? Well, as you may recall, Hogwarts has a lot of magical protections—that's why Harry is safe there. The teachers are on high alert this year for people who might want to infiltrate the castle, though, as we see when Luna and Harry are questioned upon arrival at the beginning of the school year.

Better safe than sorry, we guess.

So far so good, as far as keeping baddies out, but Draco's shenanigans with the vanishing cabinet suggest that he's working on a way to get things in and out of the castle under the radar. And if you can get things in and out…that probably means you can do the same with people. Man, we wish Draco had just gotten really into needlecraft instead.

Of course, at the end of the film, our worst fears are realized, and a pack of Death Eaters use the cabinet to breach the castle's protections and officially invade Hogwarts. Then, when Dumbledore dies, it's official: Hogwarts is no longer a safe refuge from the dangers that have been swirling around since Voldemort's return. The cabinet represents the vulnerability that's been growing and intensifying the entire film.