The harvest of Shadowchaser algae from Waterkeep fetches a high price on the open market, a fact that has not gone unnoticed by a group of river pirates who station themselves downstream from town. They attack the barges being sent to ship the algae to market.
The merchants have hired the party to deal with the threat, and make sure the algae will make it to market.
1. The pirates are not taking the algae to make a profit, but because they have discovered that it is malevolent and sentient. The Shadowchaser algae is using the pirates to spread itself around the world.
2. The pirates eat the algae which has changed and twisted them into strange ghoul like creatures. They need the algae to survive and will do whatever they must to get it.
3. The party finds the pirates’ camp, but it has already been ravaged. There was a large open tank that the pirates where using to store the algae. The walls of the tank are collapsed, and it looks like something came out of it and headed north.