Start of Darkness is lengthier than On the Origin of PCs, not just due to its page count, but also because he only focuses on two characters instead of six. In addition, while Burlew has already taken pains to give us the back stories of the protagonists, the antagonists appear to be evil for the sa...
This is the foundation of the entire story of Order of the Stick, more or less. It shows the genesis of our bad guys, and the reason our protagonists are so involved in stopping them. Its also surprisingly bittersweet, showing how guilt and fanatical drive cn utterly ruin a person... er, goblin