Yeah three is when Sirius AND Lupin come into play and its when Harry REALLY starts learning his Defense Spells to be able to fight off Voldemort and the Death Eaters. Plus it introduces Hogsmead, umm...I think this is the one where they over hear the teachers talking about Harry and the fact that Sirius was SUPPOSEDLY after him.... It's a toss up for me.....b/c I really like #3 but I really liked $5 too!