Mike Birbiglia has always been dead set against having a kid. "I was very clear when we got married," he explains early in his autobiographical solo show The New One, recounting an argument with his wife when she announced her intent to start a family. "I was very clear that I would never change," he recalls telling her.

You can probably guess what happens next, based on general life experience and the self-explanatory title of the play. As Birbiglia drolly puts it, being "very clear" with your wife about certain matters "gets you nothing. Being very clear is apparently useless."

A lot has changed in Mike Birbiglia's world since we last saw him on stage in early 2016, when his uproarious solo show Thank God for Jokes probed comedy's capacity to offend. In the years since, he's released a feature film which he wrote and directed and starred in, he's been diagnosed with Lyme disease and diabetes, and he's become a father.

Those health issues are mentioned in passing as part of his well-reasoned, seven part précis of why he should not reproduce. And he makes a persuasive case, citing his subpar genes, climate change, his possession of a cat, and the way people tend to suck, among other things. But perhaps his most telling argument is that he doesn't want his relationship with his wife, Jen, to disintegrate into something less intimate. You quickly get the sense that his opposition to parenthood is fundamentally linked to a fear that it will irrevocably alter his marriage. And of course it does, in ways he finds both dismaying and enriching.

There's another reason for his procreational reluctance: for an introspective character like Birbiglia, the decision to become a parent throws his perceived inadequacies into high relief. It forces him to confront himself in a fraught new context, one he never prepared for, in which the idiosyncratic man he's spent his life becoming must suddenly switch gears and step into the role of a father, and adapt to all the gravity of that responsibility.

Over the course of 85 minutes, Birbiglia recounts, with what appears to be unflinching candor, his struggle with the concept of parenthood, from that first fraught conversation with his wife (who he also calls Clo) to the explosive changes a baby girl unleashes upon his orderly life. Along the way, we learn all about his varicocele repair procedure (or as he calls it, "unnecessary ball surgery"), the holistic birthing education class he attends ("wasn't a great fit!"), and the extraordinary sleeping arrangements forced upon our beleaguered narrator, who you'll recall nearly died due to his REM Behavior Disorder ("now I sleep in a straightjacket in a room that's chain-locked from the inside filled with cat litter dust and super-pee").

And then there's his beloved couch, which is heartbreakingly transformed from an always reliable sanctuary to a hotly contested forbidden zone, a tightly regulated harbor where babies are welcome and road-weary, germ-infested dads are kept out at sea.

It's all very funny and bracing, because Birbiglia is a nuanced storyteller with a gift for teasing out the absurdity of contemporary American life, as well as sending up his own anxieties and neuroses. He's extremely open about his feelings of isolation that arise within the new family dynamic, and The New One is grounded in an intimate emotional honesty. That's not to say the show is a downer; it hums along on the strength of Birbiglia's warm-hearted wit, and features a boffo coup de théâtre so surprising that producer Ira Glass is begging journalists to omit it from their reviews. I certainly know better than to piss off Ira Glass, so I'll leave it at that. Just try to score a ticket. The New One may be his best one yet.

The New One continues at The Cherry Lane Theater through August 26th.