Relax. This has, or will happen, to every freelancer once. You're going to learn from it and move on. You do NOT need a lawyer. This guy knows you haven't got a

Relax. This has, or will happen, to every freelancer once. You're going to learn from it and move on. You do NOT need a lawyer. This guy knows you haven't got any way to pay damages and it's going to cost him $10k+ for his lawyer. He'll fume and threaten and make a lot of noise. Eventually, he'll go look for another sucker—I mean—inexperienced developer to take advantage of. Send an email with a sincere apology, a zip with the latest files, and a clear statement that you're unable to do anything further. Don't return any calls or emails afterwards. He might get a lawyer to send a letter. This costs $100. Ignore it. The only thing you should respond to is a court summons. You won't get one.