Predictions for Harry Potter and the Prisoner of Azkaban

I'm still somewhat in the beginning of my book Harry Potter and the Prisoner of Azkaban by J.K. Rowling and I think I could make some predictions on what's going to happen next.

  Where I am now is they are on the train goign to Hogwarts for their third year when the train goes dark and they first suspect a a power outage but Harry hears a squeaking sound and sees a tall cloaked figure. He gets engulfed in the cold from this thing that is later called 'The Dementor' (also the name of the chapter). I think the dementor was looking for Sirius Black, who earlier escaped from Azkaban which is supposedly unescapable, because once Harry woke up Ron was telling him what happened, ""and he said, 'None of us is hiding Sirius Black under our cloaks. Go.'""  The place I stopped reading was somewhat random but I do have an idea of what's going to happen next.

Previously, I thought that the new Defense Against the Dark Arts teach, Professor Lupin, was going to be an enemy, but I have changed my mind to thinking he's actually going to be a good thing for Harry and his friends. But I have been proven wrong before, for instance Professor Quirrel. But I do have a feeling he will be a very important part of the story. Also, for the ending I think the 'battle scene' will be Harry against Sirius Black. Obviously, if we're going to go with the pattern, Lord Voldemort will be teamed up with Black and try to defeat Harry. I suspect that Harry will win since there are four more books.

 Some fun facts on Azkaban