For one thing, the Spider depicted here is hardly the criminal mastermind she's built up to be. Her notes clearly reveal her identity for no discernable reason, and her tactics in the final encounter are downright stupid given that she could just run for it, especially if you have six PCs instead of four.
There are other questions too. Why is the Sailswift still in the harbor now that the slaves have been delivered? It's clearly stated that there's only one shipment a month. By the same token, why does Jarovar wander around every night when he usually has no deliveries to make?