Toad tells Mario a rumor about a secret door under the castle, and Mario tries to find it.
Toad and Mario begin telling scary stories. Then Toad tells a rumor about a hallway beneath Peach's castle (which looks like a library), the hallway contained a door; those who go in, never come out. A carpenter walked in, but was never seen again and went missing. This rumor takes place during the construction of the castle. Toad then stated that anyone who is quiet in the pillar area can hear the carpenter's sinister laughter. Mario thinks the rumor is real now. He enters the pillar room and starts to hear laughter only to find out it was just Luigi. In his anger, Mario pops him down with a hunting rifle.
Mario begins to try and find a way into the hallway and destroys the castle (or tries to) in the process. He ultimately fails. Mario decides the only way to find out if the rumor is real is to time travel. He travels to the time when the castle was nearly complete, he notices the carpenter walk into a hole where the cannon is now. Following the carpenter, he finally finds the door... He reaches for the knob, but SMG4's computer crashes. Mario fixes it and attempts to reach the knob, but he hears the workers preparing to patch the hole. Mario makes it out flying and is now titled The Flying Fatman by the workers after the adventure. Mario never got to find out what was in the door. But meanwhile, the carpenter realizes the door was just the bathroom and spent the rest of his life trapped.