You need a lawyer. They are a cost of doing business in the contracting world. If you don't have a lawyer, you're going to get run over... over and over again.
Unfortunately, it's not that simple. Maybe we (myself and the other contractors involved) have been unlucky but we haven't been able to get anything done the lawyer route. I'm happy to try again but I've realized which lawyer is important and would love a referral if you have one (my email is in my profile).
The problem may be, you're getting a lawyer after the fact. Maybe your contract sucks and you have little to no recourse. You need a lawyer up front, reviewing your contract.