Merfolk's Lullaby

Sunken Journal from Mercia, a Mystery of the Shrine of Hungering.

The Warrior was strong, though, and did not fall. On discovering who shot him, he killed the High Priest and flung him from the cliff top where he had been hiding. This story seems so familiar to me. But I am at a loss, why did the merfolk want me to come here? What great evil do they fear? It can't be related to sharks; they seem to revere them rather than fear them. Did the Warrior become a merman and somehow upset the balance of the Sea of Thieves? Or did the Ancients manage to restrain him and the Queen, and it's their return to the Sea of Thieves that the merfolk fear?