I saw "The Departed" and stayed on the edge of my seat throughout the movie. Good stuff. But I'm confused about the end of the movie. It left me with more questions than answers.

Don't read the next part of this blog if you haven't seen the movie and will be mad at me for revealing some of how it ends.

Why was whoever killing whoever? Was there really a third mole, and if so, why does he show up in the last 30 seconds of the movie? What is written on the note? What's the point?

I was disappointed at the end, but maybe a little explanation can clear this up. Can anyone help me figure out this thing?