Trapped in a realm that's not quite here, yet not quite anywhere else, Harry learns that three of his loved ones are in danger. Only by discovering his assailant's identity can he save his friends, bring criminal elements to justice, and move on himself. It would just be easier if he knew who was at risk. And had a (working) crystal ball. And access to magic. Instead, he is unable to interact with the physical world - invisible to all but a select magical few.
 
He's also not the only silent presence roaming Chicago's alleys. Hell, he put some there himself. Now, they're looking for payback.