If you still haven’t seen the wonderful Denise Fennell in the Catechism series written by Maripat Donovan and Mark Silvia, well, you need to fill that gap in your spiritual education. In these lively and sometimes improvisational one-woman shows, Fennell plays a nun giving Catholicism lessons to adults—and the results are hilarious.

The latest installment, Sister’s Back to School Catechism: The Holy Ghost and Other Terrifying Tales, takes us through the supposed Catholic origins of Halloween. As part of “taking Halloween back” and reclaiming it as a Catholic holiday, Fennell introduces us to martyrs who died violent deaths in the name of the church. I don’t want to give away too much, but if you decide to go as a saint for Halloween this year, Sister’s tips will set you right up.

A natural comedian, Fennell is not only funny, but witty and quick on her feet. She has to be—part of the charm of this show is the interaction with the audience members, and none of us are coached if she calls on our participation. (“Stand up while talking to Sister!” she shouts, much to the delight of the audience.)

In each version, no matter if it is about marriage or moral lapses, Fennell brings it. She can make us laugh about our faulty knowledge of Catholic doctrine, all while slyly satirizing or providing cultural criticism of our contemporary lifestyles, in which summer isn’t fun anymore, technology has killed how it was “back in the day,” and women dress so suggestively she has to hand them Kleenex to “cover-up.” It's funny, but there is still enough truth to all of it to give you a little pause without being preachy in a kill-joy way. That's a miracle right there.

As in the other productions, the set is an elementary schoolroom where she holds her evening catechism classes for adults. Mark Silvia both directs and takes on production design, and I loved how the walls had pictures of saints, examples of how to print the alphabet, and a photo of John F. Kennedy.

If you aren’t a Catholic, Sister will explain why you might want to be one. And she even passes candy around since this installment is about Halloween. Not only does Sister have a habit that makes her look like she came straight from the convent, there is a plot line in the second half that has a lot of comic fuel coming from the costumes that Sister has designed not only for your Halloween pleasure, but for your religious edification as well.

The result is the perfect cocktail of comedy and charm to get you through the dog days of summer until we have a little relief from the heat in the fall. You will laugh at Sister’s slamming of public school and her reminders that if you went to Catholic school, you are “a little bit better” than everyone else. You will laugh at her observations about how our kids look like pack mules when they go to school. And you will feel a little wistful for simpler times when everything was a little less intense. You simply can’t lose with this show, because Fennell, with her quick wit and withering looks, interacts with each new audience in an unpredictable way. It’s a divine experience, and I loved it.

Thru October 13. Tickets from $20. Stages Repertory Theatre, 3201 Allen Pkwy. 713-527-0123. More info and tickets at stagestheatre.com.