Ali's scar
I hope they don't do the Ali has a twin story (from the books), but if they do here's a theory:
Ali told the story about the twins in The First Secret in season 2 (read the story). Maybe the twin didn't actually stab the other twin in the chest, but in the thigh. I think the girls would notice if Ali had the scar in the past. This means that the Ali they knew before she disappeared was the evil twin, and the Ali now in season 5 is the good twin. (Of course if the scar is not that old, this theory don't hold)







