Speak to Tiffy Cashien regarding the Temple Knight base and RuneScape gold he'll take you there. You can choose to start the miniquest or simply forget about it. Your choice. Speak to Callon, the Temple Knight Commander, Callon. Callon will inform you of an investigation into the actions of the Mother Mallum, and will ask you to look into any new leads you have discovered.
You're a very attentive person, tell me, have you found any new leads? Yes, actually I don't believe you have any knowledge about Kennith? Who is he? He is a kid from Witchaven. You're now describing what happened during Kennith's Concerns. I'll call an investigation into the matter immediately. You're an Proselyte and the person closest to the situation, therefore I'll give you a fee. But I've got a bigger task. You are required to bring back a live sea slug.
It sounds like a challenge. There is a chance to get another aquatic mind control creature. If you do find one, we might be able to get a look, even though they are not directly related. To find the "other mind control creature", go to Braindeath Island via Pirate Pete and then fish for slugs and a Karamthalu similar to what you encountered in the quest. Bring it to Callon for an analysis and you'll be sent to question Kennith.
To do this take him to his room at the fish platform. Find out how he gained the powers he has during Kennith's Worries and he'll begin to scream and whine like the kid he's. Savant will be able to use his Commorb to determine if he is normal. You can return to Witchhaven and look over the yellow-skinned population. The slugs controlling them won't be receiving instructions from the Mother Mallum. It is possible that Kennith's concerns were a scheme to deter the Temple Knights and allow the Mother Mallum to escape.
Commander Callon who is back at the Temple Knight Base will inform you of a coming Treaty renewal ceremony. Security is a major concern for the Temple Knights if the Slugs attempt to control the world's most important leaders. However, that would be obvious. Instead, you'll be the host of the event and be responsible for buy RS gold observing guests' odd behavior.