The Scooby-Doo Show
While writing in his log, Uncle John noticed a mysterious Viking boat in the lake near his cabin, which he was currently living in. He stopped writing and got up to look out the window. He was then kidnapped by a Viking ghosts while he was distracted by the boat.
The gang, who was visiting Velma's uncle in order to go fishing, arrived to find the cabin empty. They found his log book and read his latest entry, which told them about a Viking boat he had been seeing. He wrote that he thought the lake was haunted. The entry abruptly stopped at the point Uncle John had gone to look out the window. On another page, the gang found several Viking Runes that Uncle John had copied into the book. They then left the cabin to search for clues.