Old diary

After defeating the Skeletal Horror You can find this in a crate near the bed in the hut of the Odd Old Man. The book explains that the Odd Old Man was working at the Varrock Museum and was on an expedition after some adventurers found some extraordinary bones. Tests revealed that the bones belonged to a creature that was alive around the end of the Third Age. He travelled to Mos Le'Harmless where he finds more bones. He remarks that the skull looks like the black masks worn by Cave Horrors. The bones seize control of his mind and he stows away on a ship but is caught by the owners and he was shackled for a week. He was then dumped into the sea not too far off the coast and swam to shore with the bones.