Arnold and Gerald go ghost hunting at night through the boarding house after finding strange glasses, supposedly belonging to the ghost of a scientist that used to live there. Does the ghost really exist or is it just one of Grandpa's made up stories?
Arnold and Gerald have a sleepover at the boarding house during a stormy night and they rummage through a box of Purdy Boys mystery novels. Arnold reaches in and finds a pair of old glasses, wondering who they belong to. Grandpa comes in with a snack for them and Arnold questions him about the glasses. Grandpa explains they belonged to Four-Eyed Jack, an old patron of the boarding house that kept to himself in his room in the cellar. He did experiments on cooking beans, which made the cellar smell terrible, and he was always trying bigger and better experiments. One day, an experiment with a pressure cooker went wrong and he died in the explosion. Now on rainy nights, the ghost of Four-Eyed Jack haunts the boarding house looking for his glasses, but he moans and bumps into things because he can't see anything. Gerald is skeptical of the story, but Arnold believes every word. Grandpa claims that since Arnold moved the glasses out of the box, Four-Eyed Jack will make his presence known. Gerald tells Arnold to put the glasses back, but Arnold wishes to find Four-Eyed Jack and give him his glasses so he will stop haunting the boarding house. Grandpa leaves to use the bathroom because he ate a raspberry cobbler that didn't agree with him, and he advises the boys to be careful with the glasses.
Arnold suddenly hears bumps, creaks and moans and is convinced Four-Eyed Jack's ghost is in the boarding house. Gerald points out that the boarding house always makes noises at night, but Arnold decides to go looking for the ghost. Gerald reluctantly tags along. They climb down the stairs and hear a loud creaking sound. Arnold thinks it's the ghost, but Gerald says it's just the bottom step that always creaks. Arnold and Gerald soon hear a strange noise and go investigate. It turns out to be Oskar and Suzie having an argument. They tell Oskar about the ghost and Oskar claims he isn't superstitious. Suzie, on the other side of the door, says Oscar is superstitious because he always keeps a horseshoe in his pants, which Oskar explains is one of his family's traditions. The three hear another noise down the hall and go investigate. It turns out to be Ernie doing some hammering in his room. They start to think there is no ghost, until Ernie says he's heard a strange noise coming from the kitchen for the past few nights, like someone "gagging on a hoagie." They hear it and walk to the kitchen. They see a shadowed figure standing over the sink and gasp as it comes closer. It turns out to be Mr. Hyunh gargling.
Suddenly, the kitchen window opens and papers swirl in the wind, taking the form of a ghost. They also hear a strange moan coming from the basement. Mr. Hyunh, who thinks ghosts are "creepy," thinks they should give it an offering. He plans on using a chicken, but Ernie says that's his lunch. Oskar advises him to use the halibut because it's going bad. They start to walk downstairs and keep hearing the weird moan. When they reach the bottom of the cellar, they realize it smells bad and the moaning is even louder. They find a door at the end of the hallway and plan to open it since the moaning is coming from behind it. Gerald thinks they shouldn't. Suddenly the door opens and they scream in fright because they think they found the ghost, but it turns out to be Grandpa. When asked why he's down there, Grandpa explains he was using the downstairs bathroom, which he keeps a secret so he can read in peace, but now the secret's out. Oskar, Ernie and Mr. Hyunh are amazed that the bathroom looks great, and are annoyed since they've had to share the crowded bathroom upstairs all these years. The gang decides there is no ghost after all and go upstairs to go to bed.
There isn't a ghost of Four-Eyed Jack after all...or is there? Later that night in Arnold's room, a ghost picks up the glasses out of sleeping Arnold's hands and puts them on, restoring his vision. He also tucks Gerald in, since the blanket fell off him. Gerald wakes up and sees Four-Eyed Jack's ghost hovering over him. Four-Eyed Jack says quietly, "Um, Boo," before leaving the boarding house, while Gerald screams loudly and wakes everyone up.