HBO’s highly anticipated prequel series IT: Welcome to Derry reached its midpoint with Episode 4, titled “The Great Swirling Apparatus of Our Planet’s Function,” delivering what may be the most grotesquely unsettling haunting in the entire Stephen King universe. The episode, which premiered on November 16, 2025 (with a UK release on November 17), featured a nightmarish sequence that pushed the boundaries of body horror and left viewers genuinely disturbed.
The Eye Horror That Defines Episode 4
Midway through the episode, the show unleashes one of the most viscerally disturbing moments in modern horror television. Marge Truman, portrayed by young actress Matilda Lawler, becomes the victim of Pennywise’s most psychologically targeted attack yet. After watching a school documentary on parasitic flatworms, Marge’s personal nightmare manifests in grotesque reality: her eyes begin to bulge outward from her face like “disembodied slugs,” swelling and expanding into multicolored stalks that threaten to consume her features.
The escalation is horrifying and relentless. Overcome with pain and panic, Marge desperately runs through the school hallways and into the shop classroom, where she attempts to sever her grotesquely swollen eyes from her face using whatever tools she can find. It’s a moment of such intense body horror that it recalls the most disturbing sequences from Stephen King’s literature while surpassing them in visual execution.
The Context: Bullying Meets Supernatural Terror
The episode establishes crucial context for understanding why Marge becomes Pennywise’s target. Throughout the episode, the formation of a new “Loser’s Club” has created tension within Lilly Bainbridge’s social circle. Lilly has bonded with new allies—Ronnie Grogan (Amanda Christine), Will Hanlon (Blake Cameron James), and Rich Santos (Arian S. Cartaya)—creating genuine friendships based on their shared supernatural experiences and mutual belief in Pennywise’s existence.
Marge, previously Lilly’s only friend, finds herself increasingly isolated and jealous of these new relationships. In response, she joins forces with the school’s cruel clique, the Pattie Cakes, to humiliate her former best friend. The plan involves convincing Lilly that a popular boy has romantic interest in her, setting up a cruel public embarrassment scheme reminiscent of King’s Carrie.
However, as Marge follows Lilly to the bathroom to ensure the humiliation proceeds, she experiences a moment of conscience. She begins to confess the truth to her friend—and that’s precisely when Pennywise strikes, weaponizing her moment of vulnerability and moral clarity.
The Genius of Pennywise’s Manifestation
The brilliance of this sequence lies in how Pennywise exploits Marge’s deepest psychological fears. In the very first episode of IT: Welcome to Derry, Marge expressed anxiety about her new glasses, worried that they made her eyes look too large. Pennywise has been observing, waiting, and now transforms that insecurity into a nightmare that seems inescapable.
Rather than merely threatening physical violence, It manifests as a parasite that bloats and distorts Marge’s eyes—turning her self-consciousness into literal body horror. The creature doesn’t simply attack; it weaponizes fear itself, making the victim’s own body the source of terror.
Behind-the-Scenes Commitment and Performance
Matilda Lawler’s portrayal of Marge’s terror demonstrates extraordinary commitment to the craft. When asked about filming the grueling sequence, Lawler candidly expressed her own shock: “No. I had the same reaction. I was like, ‘Girl, please, please, please, no!’ But it was honestly a blast to film that.”
The production design for the scene required innovative practical effects work. Lawler explained: “The way that we filmed it, I was wearing like a half head of prosthetics. So I had like a prosthetic piece that they put on and then they would attach these little wires into the hole of my eye or the hole of the prosthetic, and the wires would just stick out. So I was basically like running down hallways, screaming, crying over these wires coming out of my eyes.”
Despite the surreal experience of filming such an intense sequence, Lawler emerged pleased with the results: “I think it turned out well. I love how the CGI looks and it was just a blast at the end with Clara coming in. We got to have a really good time with all the blood spraying on me and that like physical action of like you trying to rip it out of my hand. I just remember that being an intense, but very fun scene.”
Co-star Blake Cameron James offered high praise for Lawler’s professionalism: “I’ll say something about Tilly: She commits to her character not only probably more than any child actor I’ve ever worked with, but any adult actor or actress I’ve ever worked with. Like she really, really, really gets like in and she just commits fully 100%. That’s a skill.”
The Broader Episode: Investigation and Mythology Deepens
Beyond Marge’s horrifying encounter with It, Episode 4 advances the central plot significantly. The kids’ attempt to prove Hank Grogan’s innocence through photographic evidence fails when police discover the supernatural elements have vanished from the pictures. Meanwhile, Will Hanlon experiences his own terrifying attack while fishing with his father—being dragged underwater by a burned corpse—leaving physical scratch marks that provide evidence his story might be true.
The episode also features an extraordinary revelation about Derry’s mythology. Dick Hallorann, portrayed by Chris Chalk, psychically torments a Native American character named Taniel (Joshua Odjick) to extract information about the origins of Pennywise and the location of what they call the “weapon”—thirteen pillars believed to keep Pennywise trapped in Derry. The psychic torture scenes provide crucial worldbuilding, expanding the Stephen King universe’s mythology in unexpected ways.
The episode’s final moments reveal a crucial location: the decrepit house on Neibolt Street, the Well House, which serves as the entrance to the tunnels containing those thirteen pillars. This location recurs throughout the IT franchise, appearing in both the 2017 and 2019 films, establishing crucial continuity within Warner Bros.’ Stephen King cinematic universe.
Release Schedule and Where to Watch
IT: Welcome to Derry continues its weekly release schedule with new episodes arriving every Sunday. Episode 4 premiered on HBO and Max on November 16, 2025, at 9:00 pm ET/6:00 pm PT. UK viewers accessed the episode through Sky Atlantic on November 17, 2025, at 2:00 am GMT, with a repeat airing at 9:00 pm, and streaming availability through NOW.
The remaining episode schedule for Season 1 is as follows:
- Episode 5: November 23, 2025
- Episode 6: November 30, 2025
- Episode 7: December 7, 2025
- Episode 8 (Season Finale): December 14, 2025
For access to IT: Welcome to Derry, viewers can stream through HBO Max in the United States or through Sky Atlantic and NOW in the United Kingdom
