Last summer I had a chance to strike a deal with the devil.

I sat, contemplating my choice — what I could live without to acquire the one thing I most desired. This was no arbitrary crossroads. Over the past 40 or so minutes I had confessed long-held goals and romantic yearnings while revealing details of my most intimate relationships. They were now being weighed against me. All, I was told, could be mine, minus what I would sacrifice. The contract would be binding, necessitating a drop of blood.

I was left alone, a tiny lancet sitting before me. The barely audible cackle of candle kept me company in a stark warehouse room, a setting that felt illicit while the small flame’s fragility reminded me that I needed to make a decision.

I was here because I had booked a session with Yannick Trapman-O’Brien’s “Undersigned,” a show he bills as a “psychological thriller for one.” Each production is personal, and highly individualized to its participant — plot points detailed here may not unveil for every guest. Know, however, there is no talk of dooming oneself to a fantastical afterlife. “Undersigned” is grounded in our reality, a conversation we have over our wants and needs, and, at least for me, what aspects of my personality or social circle I would forgo to achieve them. Love and various relationships were on the table as I fiddled with the lancet and considered puncturing my finger.

This was not a decision I would make lightly. Trapman-O’Brien’s performance, after all, had created an atmosphere of damning seriousness. And I hadn’t even seen him.

For most of the show I was blindfolded as he sat across from me, and he had left the space while I raced through my life and the future I was starting to imagine for myself. It’s rare to partake in “Undersigned” — after bringing it to L.A. last August, when I experienced it, Philadelphia-based Trapman-O’Brien is back with a smattering of dates this month. Limited tickets, at the time of writing, remain.

Despite being comfortable with vulnerability and having a tendency at times to overshare, I went in to “Undersigned” with trepidation. No topic, unless specifically requested, is off limits. Our relationship to money, sex, religion, love, power and more are all fair game, and the subjects are discussed in a setting that nods to the occult. Yet “Undersigned” ultimately became something akin to a therapy session, as I was prompted to analyze my strengths and weaknesses in matters of romance and faith.

Trapman-O’Brien, 32, has a unique ability to improvise, to quickly twist my words and use them against me. There were no cards or magic tricks here. “Undersigned” is purely a meeting of the minds, and those who treat it seriously will find it most revealing.

My session was a tug-of-war between empathetic and selfish tendencies; I wanted no deal, I said, unless all those potentially affected were happy, but such a request necessitated taking a figurative scalpel to other areas of contentment. Thus it became a work of self-examination. If rewriting history and one’s life were possible, how much could I accept while still looking at myself in the mirror?

Only everything started to become twisted. I had gone in expecting to share some of my professional and romantic dreams. As the show progressed, however, a fear that I would never achieve them set in.

“There is an enormous act of care in providing people a place where they can be confronted by themselves,” Trapman-O’Brien says. “For all that the themes and origins of this story are rooted in traditions and in things that are bad and sinister, I actually find it to be an incredibly affirming piece to do. I am gobsmacked by people’s generosity, and courage to stare down a scary thing. I’ve had people say something and then immediately say, ‘Oh, I don’t like that that’s true.’”

Trapman-O’Brien is careful with his words. A promise of “Undersigned” is that what is spoken of during the performance will never again be discussed. He will reveal, only broadly, the topics that have been broached. A veteran of the East Coast participatory theater scene, Trapman-O’Brien’s prior show, “The Telelibrary,” was born out of the COVID-19 pandemic, a whimsical yet open-hearted telephone-based performance in which vocal prompts led us either to literary reflections or to recollections left behind by other callers.

“Undersigned” started in 2019 as a commission for a patron’s Halloween party. Trapman-O’Brien balked, not wanting to create a horror-themed show, but then became intrigued by exploring the concept of making a deal with the devil. “Undersigned” only works because the choices don’t feel like an arbitrary thought experiment; that is, it’s not a game of accepting, say, untold billions by giving up a pet or a limb. Throughout, the blindfolded conversation with Trapman-O’Brien dials in on our emotional wants and needs, and then needles away at them in search of their root.

The goal? To emotionally disarm guests by creating, in Trapman-O’Brien’s words, a “nonjudgmental space.”

“One of the problems is the second you open up the idea of a deal with the devil, people expect that they’re going to get screwed,” Trapman-O’Brien says. “I find people negotiate against themselves. One of the most impactful things of the piece is talking to people about why they keep accepting less than they want. Like, ‘I don’t need my dream job. I just need a good job.’ But I told you that you could have anything you want. Have your dream.”

The vulnerability inherent in the show extends to its payment structure. An “Undersigned” performance asks for a “down payment” of $100, with slightly cheaper options for students and creative professionals. At the end of the show, guests are presented with a notebook to write something personal to leave behind for others to read, and an envelope containing 30% of their initial investment in cash — a recognition, reads “Undersigned’s” fine print, of “the gamble” guests are taking with such an openly revealing, potentially unnerving show.

“I think the best way to ask for something is to invite,” Trapman-O’Brien says. “And the best way to invite people into vulnerability is with vulnerability of your own. We’ve talked about how heavy the show is. And I believe a big part of what makes people willing to share is that I try to find as many places as possible to stick my neck out. “

Trapman-O’Brien says he regularly hears from those who participate, sometimes months later, with updates on their agreement. For me, I sat in the warehouse’s lobby — the show is run out of Hatch Escapes in Arlington Heights — for a good 45 to 50 minutes, contemplating how easily I was willing to offer up professional ambitions and personal connections for something I believed would make me happy.

“There’s a non-zero number of participants,” Trapman-O’Brien says, “who will reach out and say, ‘I know I’m not supposed to discuss it, but it did happen.’ Well, those rules are about your safety and mine, so I can say, ‘I don’t know what you’re talking about.’ But that to me is what it means to do a piece in which you say things that you need. Some of them might surprise you.”

Arguably, the biggest revelation for me with “Undersigned” is how true it all felt. About six months after I partook in the production, there are moments I’ll catch myself thinking about the show and the choice I was presented with. Should that future I imagined for myself ever become a reality, a not insignificant part of me will wonder what other forces were at play.

For when I departed “Undersigned,” I also left a part of me behind: a drop of blood, and a signed deal with the devil.