After Duane Comack and Stephanie Alpert are let out of Hill House for leaving the tour group to hunt for the missing head of Andrew Craw, they meet a kid their age wearing a turtleneck sweater named Seth that they first saw in the tour. Seth claims to have snuck into Hill House at night, and helps the two sneak back in to hunt for the head. He also tells them a story about a boy who died inside the house's dumbwaiter. When they arrive in the pantry, Seth locks the door on them. He then claims to be Andrew Craw and that he needs a new head. He goes after Duane, trying to pull his head off his shoulders, until Duane and Stephanie manage to find a hidden passageway which leads them to the head of the real Andrew Craw. The ghost of Andrew arrives to thank them for finding his head so that he can finally rest in peace. Seth is frightened over the whole situation. Otto, one of the tour guides, arrives and reveals that Seth is his nephew, and is known for telling ghost stories.
Several months later, during the middle of winter, Duane and Stephanie decide to return to Hill House for one more tour. They are greeted by Otto and another tour guide named Edna, and the tour goes as normal. However, upon leaving, the kids are stopped by a pair of cops, curious as to why the kids are leaving Hill House. The cops tell Duane and Stephanie that Hill House has been abandoned for months. Duane and Stephanie take one last look at the house and see the ghosts of Otto and Edna staring at them from a window. However, Seth's status remains unknown.
Similar to the episode, Seth helps Duane and Stephanie get back into Hill House after it closes to hunt for Andrew Craw's head. He tells a different version of the dumbwaiter story than in the book, how the boy who once lived in Hill House would eat nothing but ice cream. But when the dumbwaiter got stuck, he leaned too far into the shaft and fell to his death. He then leads Duane and Stephanie into the attic where the art supplies of the ghost of the sea captain that built Hill House still remain. He tells them that whoever the captain painted would turn into a ghost. He then claims to be Andrew Craw and starts to go after Duane's head. Suddenly, the three find the real Andrew's head inside the dumbwaiter.
As Otto arrives, he tells the two that Seth works for him. Otto lets Duane leave, but keeps Stephanie for a while. He then reveals himself to be the ghost of the sea captain, while Seth is revealed to be the ghost of the ice cream boy. Otto, Seth and Andrew all live together in Hill House. Otto then begins to paint Stephanie's portrait as punishment for disrespecting the house, causing her body to vanish with every part he paints. before Duane returns to the attic and saves her just before Otto can finish the portrait. Otto chases Duane and Stephanie until they escape Hill House and run away.
Some time after that night, Hill House stops giving tours. Otto shows off the now boarded up Hill House to a couple looking to purchase it as a fixer upper. He promises them that they'll be very happy here as he shuts the door with a sinister expression on his face. As he shuts the door, the door knocker's eyes begin to glow.
Seth is described as having wavy blond hair and wearing blue jeans and a long black turtleneck sweater that covers his entire neck.
Seth has a highly confident attitude to him, especially when he mentions going into Hill House at night on his own. He is also revealed to be a prankster who enjoys scaring others, evident when he pretends to be Andrew Craw to scare Duane and Stephanie. The episode version remains mostly the same, but adds in a new backstory of Seth being the ghost of the ice cream boy. He has an insatiable appetite for ice cream, but refuses to share any, much to Andrew's chagrin.
- Seth's actor, Sean Ryan, played Buzz Crocker in the very first Are You Afraid of the Dark? episode "The Tale of the Phantom Cab".
- The book leaves it uncertain if Seth had died alongside Otto and Edna after the events of the story, or if the three were ghosts the entire time.