Flotsam is the biggest side quest that you will be able to tackle before leaving Caldera for the pirate island of Tacarigua. You will obtain this quest by speaking with the merchant captain by the store house. You can find the store house (the very same one that the prisoner from earlier was attempting to steal from) by the stairs to the beach, only to the left instead of to the right. Head over and speak with the NPC, whose official name will be simply Storehouse Master. He will note that a lot of junk washed up on the shore after the Kraken sunk the ship just offshore. Some of the items contained within the washed up cargo, he notes, may be valuable. You would be doing him a great service by going down to the beach and collecting the various pieces of cargo that washed up onto the beach. Agree to help him out.
You will need to collect a total of six pieces of cargo in order to please the Storehouse Master. The cargo, luckily, is pretty easy to spot. It will come in the form of medium sized wooden boxes half buried in sand. Head back up the stairs and go straight across and down to reach the beach. As you make your way towards the beach, you will be reminded of the hostile wildlife. Sand Devils will attack you as you make your way deeper into the beach, but for now you should be safe. Don’t draw your sword just yet, as drawing your sword will make the interaction icons disappear from the screen, replaced by sword attacks. The first five crates will be strewn along the shoreline, so simply walk a straight path along the shore to find them and pick them up when prompted. The final crate will be all the way to the far side of the beach and back, a little deeper up the shore than the others were. As you approach it, a group of two Sand Devils will emerge from the ground and attack you.
If you can, go for the first strike on these small enemies. Even though the Sand Devils are tiny and relatively weak, if you find yourself caught between both of their attacks at the same time you can still wind up missing a lot of health. Hack away at the first Sand Devil with rapid sword attacks, but watch out for the second enemy, who may try to get behind you and surprise you. Alternate attacks from one enemy to the other and back again if this turns out to be the case. This will stun both Sand Devils long enough that you won’t have to worry about one of them attacking you while you turn to fight the other.
After you kill the two Sand Devils, loot the treasure from the flotsam. You will now have collected enough of the washed up merchandise to please the Storehouse Master. Note that there is a little cave embedded in the face of the cliff behind you. Although there is nothing of real value in here, the sights inside are ethereal and pretty, and you will be able to kill two more Sand Devils, thus gaining a bit more in the way of experience points (called Glory in Risen 2.) If you decide to go into the cave, hug the right wall as it loops around the central stones. The two Sand Devils will emerge from the watery ground on the right side of the loop and attack you. Use a similar strategy to the one that you used to kill the last group of enemies to finish these Sand Devils off, too.
Now that you have thoroughly explored the beach, climb back up the stone staircase and return to the merchant with his goods. He will reward you with 50 Glory points.