Harry receives the invisibility cloak at Christmas, from a mysterious gift-giver who, for now at least, remains anonymous. When he puts it on, he vanishes from view. Like a lot of things in Harry's life, the note that accompanies his present answers his questions, but leaves another fistful in its place:

HARRY [reading]: Your father left this in my possession before he died. It is time it was returned to you. Use it well.

Questions aside—how do you "use it well," exactly?—hey, it's an invisibility cloak. We wish we had one.

Like so many magical items in Rowling's universe, there's more to the cloak than meets the eye, but in The Sorcerer's Stone it's just a nifty tool to overcome obstacles in Harry's way.

In this case, said obstacle is Filch, who could catch Harry wandering around after hours and put a serious crimp in his efforts to find the Sorcerer's Stone. Good thing Harry has friends who like him…and who know just what to get him for Christmas.