The Old Castle's Secret

The Old Castle's Secret is a Donald Duck story written by Carl Barks. Besides having status as one of Barks' best stories, The Old Castle's Secret is also notable for being Donald and Huey, Dewey and Louie's first treasure hunt with their uncle, Scrooge McDuck.

Plot
Scrooge McDuck, in his second appearance, recruits his nephews to search for a family treasure back in Dismal Downs, the old castle of The Clan McDuck, built in the middle of a swamp in Scotland. The treasure once belonged to Sir Quackly McDuck, but both the treasure and its owner disappeared during the siege of 1057. The Clan has been searching for the treasure for centuries but Scrooge, the last McDuck, thinks that he can locate it thanks to an X-Ray machine that can look behind/through the castle's walls. Finding the treasure proves to be the easy part of the mission. But they have to face a mysterious ghost that steals the treasure from them and repeatedly tries to dispose of them. They can't see it but they can see its shadow; the shadow of a skeleton. During this, Scottie the caretaker of the castle, seems to have been murdered by Sir Quackly, and Scrooge, Donald, and the Nephews are trapped on a locked battlement. The Nephews escape by swinging across into the surrounding moat, but can't get in. However, they then remember the tale of Sir Swamphole McDuck, who sealed the dungeons (due to the costly price of running a dungeon) and find a secret passageway into the dungeons and castle through his fake grave site (while his skeleton was located inside of his armor), which had been made in case there was a need of emergency evacuation of the castle. Scrooge and Donald are remain on the battlement until Scrooge reveals he has a gun (which can shoot the lock and unlock the door), where Scrooge, embarrassed, first tells Donald to give him, "a good, swift, kick!". While in the dungeon, the Nephews find the treasure box, but are nearly attacked by the ghost, and find the other way out of the dungeon; the pillar that Sir Swamphole's armor is resting on is actually a door. Scrooge, Donald, and Huey, Dewey, and Louie (who have found the invisibility spray) give chase to the ghost through the swamp (who can be seen since he's covered in mud), and the Nephews and Donald tackle him to the ground, retrieving the treasure box. The ghost is revealed to be a thief who was impersonating Scottie (who had died of old age years before) using a special spray-like formula that made him invisible but did not prevent his skeleton from casting a shadow. After that, Donald then takes all of the kids's credit (who didn't realize the invisibility spray even existed). Enraged, the kids then trick Donald into thinking the spray is a mosquito repellent, where they then make him completely invisible (save his tail and legs).

Analysis
The story is usually referred to as one of Barks' most memorable for a number of reasons. The plot borrows elements of horror and mystery stories, favorites of Barks, such as the old and mostly abandoned castle with dark halls, hidden dungeons and crypts, ancestors' skeletons buried inside the castle, the old McDuck cemetery with the graves of entire generations of the main characters' ancestors, the misty swamp, the threatening "ghost" and the eminent danger that the characters feel around them. Barks put an effort into the details of every panel so that they gave a sense of melancholy suitable for this rather moody story and he used pictures of old Scottish castles as drawing references to add to the story's realism. It is considered among his best drawing efforts.

The story marks the second appearance of Scrooge in a story but the first where he acts as the leader in a treasure expedition, a theme that Barks would later use often and is currently considered traditional for an Uncle Scrooge story. It introduces the Clan McDuck, giving a family history to the characters that would later be expanded by both Barks and his "successors" and firmly setting the character's origin in Scotland, a homeland where a number of later stories would take place. Dismal Downs itself has been used as a setting for other stories and its history and architecture expanded.