Sea Slug

The Fishing Platform
Talk to Caroline near the town of Yanille, south of East Ardougne, who will tell you her husband, Kent, and son, Kennith, are missing. She will ask you to go to the Fishing Platform to find them. Holgart has a boat that he can maybe take you in.

Talk to Holgart, and he will tell you his ship is in need of repairs. He will ask you to go and get him one hundred swamp paste to fix it up. Once you give him the swamp paste, Holgart will appear in a cut scene fixing the boat. Talk to him again to go to the Fishing Platform.

Investigate
When you arrive you will notice the odd behaviour of anyone, as they all seem to be in a zombie-like trance.

Look around and find Bailey inside a small room on the platform to the west and talk to him. He will tell you about the odd happenings and the hauling up of the sea slugs. Also, pick up the broken glass in the northwest room for later in the quest.

Helping Kennith
Go to the ladder in the north east corner of the platform, and pick up some of the damp sticks near the ladder. Climb the ladder once you are ready, and look around if you wish. In a room on the west side, past the crane, you will find Kennith. After talking to him he is too horrified to leave with all the sea slugs and the strange fishermen. He will tell you to find his father, Kent, and to hurry and help him.

Go back to Holgart and talk to him where you arrived there. He will take you to a deserted island, where you will find Kent all alone. Talk to him, and hear his story about the sea slugs and how he really is trying to help Kennith then ask Holgart to take you back to the platform. Try to climb up the ladder. The Platform fishermen, possessed by the sea slugs, will stop you. Talk to Bailey to find out the slugs weakness. He will give you an unlit torch as they are afraid of smoke.

Use the broken glass on the damp sticks to make dry sticks, then rub them together to light the torch. Climb up the ladder again, and talk to Kennith. From outside the room, kick the badly-repaired wall (east facing, north end) to make an opening. Talk to Kennith again, then rotate the crane to save him, shown in a cut scene. Talk to Holgart again to return to shore. Finally, talk to Caroline to finish the quest.

Reward

 * 1 quest point
 * 7175 Fishing experience
 * Access to the Fishing Platform
 * Oyster pearls

Trivia
When using a unlit torch on a Sea Slug or a Fisherman, it made a glitch as if fire was being stretched.