This was a bit confusing, I kept restarting as I was getting hardstuck at 36% - this worked for me.
Pick up the quest and talk to Athelton Jones a 2nd time - your progress bar won't move.
Talk to Ellanoir and follow the prompt she gives you.
Talk to Duryllin and follow both his prompts.
Talk to Juddison Rakes and follow him prompt.
Talk to Ellanoir again and follow her new 2nd prompt.
You should now be at 48%.
Go to the beach at /way 65, 59. Make sure your Torch of Pyrreth and Idol of Ohn'ahra are both on when you click this to read where to go next.
Walk down the beach with both toys still in use, you'll be able to investigate sandpiles to see different things - these won't move up your progress bar. The important part is not anything you find within them, but if you can't see them - you have missed a step. It's a good mid way checkpoint to make sure that you're at the right stage for the next step.
Go to /way 66, 40. Through the tunnel to find the body of Herrkrop - you should now be at 60%. You will see Athelton Jones again, you can talk to him but he won't say anything useful or move up your progress bar. Ignore him saying he doubted anyone here saw anything.
Talk to Nat Pagle and follow his prompt.
Talk to Julia Henning and follow her prompt.
Talk to Scrapes and follow his prompts.
You should now be at 96%
Go back to Athelton Jones behind Scrapes and tell him you think it was Scrapes. Scrapes will then go into the boat and run away - congrats you've completed this quest.