Similar to a formula he’s mastered in books, Indianapolis author John Green balanced topics heavy and light Thursday night at Pike Performing Arts Center.

Green attracted a sold-out audience of 1,500 for the hometown stop of a tour promoting "Turtles All the Way Down," his new novel that depicts obsessive-compulsive disorder as experienced by a 16-year-old girl.

It's a mental health diagnosis Green shares with fictional protagonist Aza Holmes.

A missing-person mystery set in Indianapolis, "Turtles All the Way Down," details "thought spirals" that hinder Aza's moment-to-moment existence.

Green talked about his personal struggles to articulate obsessive-compulsive disorder during Thursday's opening.

"It felt like all the time there was a real monster, an actual monster, that lived inside of me," he said. "It felt like I was trapped inside a prison cell the exact size and shape of myself. ... Most of all it made me feel like I was a passenger in my own consciousness."

He's found effective treatment by taking prescribed medicine as directed, through cognitive behavior therapy and by ramping up physical activity (Green is the upcoming subject of a Runner's World magazine profile).

At the same time, he's described his brain as a "liar" that can undermine his wellness.

"How do you form a sense of self while there is within you this kind of unreliable narrator of yourself that's telling you that you need to be afraid of stuff you don't need to be afraid of, that's telling you to despair, that's telling you whatever," Green asked during a backstage interview before the event.

"It's really difficult, for me at least, to figure out, 'Well, what do I mean when I talk about myself? And how can I have a definition of myself that makes sense to me, that makes me feel like a singular noun while at the same time excluding these intrusive thoughts that play such a big role in my daily life?' "

"Turtles All the Way Down" is Green's first novel since 2012's "The Fault in Our Stars," a book that sold more than 23 million copies worldwide and later was made into a movie.

Thursday's audience included Chelsey Lang, a middle-school science teacher who wore a T-shirt advertising "Dear Hank & John," Green's weekly podcast with his brother, Hank Green, and a jacket from NerdCon: Nerdfighteria, a 2017 Boston convention for fans of the the Green brothers.

Lang said she appreciated John Green's openness in writing and talking about OCD.

"There's a lot of fantasy elements in young adult literature," Lang said. "But it's good to have something people can connect with, whether they have a mental illness or not, and build more empathy around it."

Not to be confused with a medical lecture, the program also delivered laughs. Green, the 40-year-old father of a 7-year-old son and 4-year-old daughter, joked about eating the crusts of 400 grilled cheese sandwiches and his artistic appreciation of animated film "Penguins of Madagascar."

In a wry aside, he advised teenagers to avoid resolution of emotional problems: "Always bury it down and deal with it in 30 years."

That remark arrived during Thursday's live version of the "Dear Hank & John" podcast, a program that bills itself as two brothers answering questions and giving dubious advice.

Normally, the podcast is made by John in Indianapolis and Hank in his hometown of Missoula, Mont. For the 19-city "Turtles All the Way Down" tour, Hank is an in-person co-star who sings original songs about science and wears a turtle costume for a comedic sketch based on phylogeny and taxonomy.

The Green siblings, who grew up in Orlando, Fla., built an online empire on "Vlogbrothers" — their 10-year-old YouTube series in which they exchange 4-minute video messages for each other and an audience of 3 million subscribers.

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Indianapolis, where John Green was born and his home since 2007, receives ample exposure in "Vlogbrothers" episodes.

"The Fault in Our Stars" was a story set in Indianapolis and Amsterdam, and the entirety of "Turtles All the Way Down" is set in Indianapolis.

Green told the Pike audience he's not presently interested in writing stories that unfold anywhere else.

"I just find this place really fascinating," he said. "It's so American in the best and worst ways."

Green said Pogue's Run and the White River rank as his favorite Indianapolis references in "Turtles All the Way Down."

"I love the White River," he said before Thursday's show. "I was a little hard on it. But I guess I wanted to get at what I love about it. ... It's so pristine and abandoned and empty. You see foxes and deer and coyote when you're kayaking on the river all the time. There are turtles everywhere. And it's like that only because it's so polluted."

Call IndyStar reporter David Lindquist at (317) 444-6404. Follow him on Twitter: @317Lindquist.