Ask HN: Need advice, I'm getting sued.

Do not say one more word on the subject. Not in writing, not in public, not even to your friends over beers, until you get a lawyer. Think of it like the Miranda rule -- now that a legal dispute has arisen, anything you say can and will be used by them against you.

What you shouldn't do now is panic. They've sent you a letter demanding a large sum of money? Big deal, anyone can send a letter. It's not unusual for people to try to bully others by having their lawyer draft a letter full of scary-sounding language that, when parsed by a lawyer, actually says nothing. These people hope you will read the letter, panic, and do something stupid like trying to settle with them before talking to a lawyer.

Don't give them what they want. Get a lawyer.

Ultimately this comes down to your contract with them. You did have them agree to a contract detailing everything right??

Although some will say a contract is worth as much as the paper it's written on (or how much one is willing to pay a prosecutor) it's still smart to outline expectations from both sides before beginning work.

I'm curious though -- define "insane amount of money".

Also, what went wrong? Unmet expectations? Better offer come along? Burn out?

Get an attorney, who'll probably advise you to seek an out of court settlement, if possible.