[This story contains major spoilers for Swarm season one, episode four “Running Scared.”]

Swarm, co-created and co-executive produced by Janine Nabers and Donald Glover, features a slew of celebrity cameos, including Rory Culkin and Paris Jackson. But episode four’s celebrity guest star — the Grammy-winning Billie Eilish — has delivered one of the series’ buzziest appearances.

Set between 2016 and 2018, Swarm follows Dre (Dominique Fishback), a fan of the fictional Beyoncé-esque music icon Ni’Jah, whose love for her favorite singer crosses the line from obsessive to murderous. After setting off on a cross-country journey, she meets a slew of characters — and commits a slew of crimes.

Alongside killing a string of haters in the name of her icon, Dre hits the road to see her favorite star at Bonnaroo despite not having a wristband, but gets pulled over in Tennessee by a racist cop.

While trying to get him off her tail at a gas station, a young white woman comes to her rescue, with Dre following her back to a compound full of more seemingly friendly women. It’s a group led by Eilish’s Eva, whose warm and inviting nature hides something more sinister underneath.

Eilish, who is in her acting debut, was suggested by Swarm casting director Carmen Cuba, Nabers told The Hollywood Reporter (Nabers’ full interview publishes on Monday). “When she pitched [Billie Eilish] for the role of Eva, we were like, ‘Oh, she’s really cool! Let’s go with it!’ And it worked out,” said Nabers. “She was great!”

While Eva says she “feels so drawn” to Dre and suggests she’s “part of the tribe now,” it becomes clear as Dre spends more time that Eva’s setup is less a commune and more a cult. The women wear the same colors and share the same body brands. Eva, the “female empowerment” group’s executive director, hosts training and healing sessions with Dre, who gets lured in following a hike.

It’s reminiscent of several Hollywood-adjacent cults, most clearly the NXIVM cult, which involved actresses like Alison Mack, who is currently serving a three-year prison sentence. Nabers has said Eilish’s character was inspired by that cult and it’s leader Keith Raniere, who was sentenced to 120 years in prison and fined $1,750,000 in the high-profile sex-trafficking case.

“There is a cult that existed in the world that was very prominent during that time,” Nabers tells THR, referencing NXIVM (see THR‘s 2018 cover story on Mack and NXIVM). “And that is the kind of true-crime element to that episode. And I think that when people think of the idea of artists or celebrities, there is this idea of thinking about the cult of Taylor Swift, or the cult of the Beatles or whatever. What we were really interested in was just seeing someone who worships at the altar of ‘something,’ and (exploring) this idea of what is the cult of the mind.”

Eventually, Eva’s entrancing aura turns dark, her manipulations of Ni’Jah’s biggest fan pivoting to unsettling threats after Dre begins to seriously question the women she’s surrounded by. After their attempts to isolate her through meditative sessions, taking her phone and cleaning the blood from one of her murders out of her car’s backseat, Dre decides it’s time to move on even if Eva doesn’t agree.

The result in Eilish’s Eva getting run over multiple times by Dre, along with several of her cult members.

Fishback told Rolling Stone the singer was “respectful of the craft” and “came in with ideas, wanting to talk about it, being game to rehearse,” with the actress adding that the “Eva character essentially asks for it.”