There's an old woman slightly apart from the festivity outside the tower. She's the only one who will speak to you. She can help you enter the tower, she says; she knows who did this and his magic is more powerful than hers, but she knows how to get around it.

Here is what you must do:

There are two chests somewhere in this city. They contain the bodies of the last two abducted people the wizard tried this with. You will need to find those chests, open them, and reassemble the bodies; they will tell you where to find the keys to the tower. After that, you must somehow find a way to exit the tower without any of the people outside noticing, because they will stop you if they do - by killing you just like the last two...

You must hurry; we're all running out of time.