Invitation is a Document in Rise of the Tomb Raider. It belongs to the Journal of Lord Croft set and contains Lara's father's research note and other, more personal messages to Lara. They mainly cover his problems with his research after his work was discredited as a fools errand.
But the point of this work is not to keep it in the shadows. The point is to expose it. To help bring the truth to the world.
Amelia believed that it was noble to face adversity head on. That strength was born from inside oneself. She was right. She was always right...For better or worse, I will accept the invitation.