Angel considered his options. His crew had all refused Wolfram and Hart's offer, tempting as it was. But this could save Conner, was probably the only way to save him. Lilah saw his doubts, everything was negotiable, she decided to make a different offer.
Lilah; Whether you join us or fight us, we need you to help save the world with the amulet. As for Conner, we can still give him a normal life, and you can leave here with no obligations.
Angel: What's the catch?
Lilah: You sign away all rights to the Shanshu prophecy. As long as you live, and that could be centuries, you'll always be a vampire.
Angel: What makes you think I won't be fighting you for eternity?
Lilah: Eternity is a long time Angel. I'm sure you will be fighting against evil at times. At other times you'll fight for evil. It's one way for me to amuse myself for eternity, as you lose all hope of a normal life.
Angel: I agree to this, Conner gets a normal life and family? He'll never remember me or Holtz, the things he did?
Lilah: No, he'll never know you ever existed. Just sign this contract, then you can go save the world for, what I wish I could say was the last time.
Angel read the contract, it said exactly what Lilah said it did, nothing about Angel selling his soul or joining Wolfram and Hart. This wasn't an easy decision for him, but it had to be done. Finally Angel grabbed a pen to sign the document. Lilah grabbed the pen and stabbed Angel's hand with it. She informed Angel that the contract had to be signed in blood. Angel complied. He gave away his hope to save Conner.