I need to walk away from house, I paid four hundred thousand and it is now (after just 2 years) worth a little over two hundred thousand. What can I expect if I do walk away.

You can expect for the Mortgage Holder to aggressively pursue you for the default on your loan.

They may come after you themselves, or they may sell or assign your debt to an agency.

I assume this is going to leave you with a substantial balance due.

I would expect them to sue you for this balance.

There is no rush to do anything, yet. They may let you walk away, or they may pursue you for the deficiency if the home doesn't sell and payoff the note. Start checking into Chapter 7 and Chapter 13; one of them may help you, but in the mean time, do not worry yourself sick. It won't help, anyway. Some further info: Bankruptcy Chapter 7 Personal Consumer Creditors File and Bankruptcy Chapter 13 Debt Payment Retain Assets