Credit: Handout photo by Margot Schulman

British playwright Bathsheba Doran’s The Mystery of Love & Sex is a sort of thought experiment: If there were a community in America where the chirpy white daughter of a lapsed Southern Baptist and a secular Jew could grow up being best friends with the shy black son of an Evangelical Christian, what would their relationship look like as they crossed the sea of early adulthood together? The unlikelihood of their pairing gives Doran’s warm and unpredictable 2015 comic drama a nagging lack of specificity, one it eventually manages to shake—mostly—thanks to the brio of the four central performances in Stella Powell-Jones’ production for Signature Theatre. Signature’s 275-seat Max space feels like a big room for a play this intimate, with the audience surrounding the cast on three sides.

Shayna Blass plays Charlotte, a girl who seems to verbalize her every sexual impulse to her virginal best pal Jonny. In the show’s first scene, the pair are in college and seemingly cohabitating as Charlotte’s parents (Jeff Still and Emily Townley, both empathetic and funny) arrive for dinner. They want to know, as parents will, if Charlotte and Jonny are a couple now, and Charlotte is impatient to iron that out, too. Propositioning her oldest friend, she asks him, “Doesn’t it feel inevitable to you?” In fact, the bond she and Jonny (Xavier Scott Evans, channeling Jonny’s anxiety so fully it hurts to look at him) seems more sibling-like than platonic or sexual; the way their rapport shifts as each party tries to pin down their sexual identity, and the relationship between Charlotte’s mother and father comes more sharply into focus, becomes the substance of the evening.

Weirdly, Doran has given only her male characters professions: Howard, Charlotte’s father, is the author of a popular series of crime novels, while Jonny publishes a memoir and becomes an academic. In the absence of a father, both Howard the man and Howard’s fiction turn out to have a profound and unforeseen influence on Jonny. To say more would be to deprive you of the show’s richest pleasure: discovering the way the joy and the obligation of family will assert itself, even when you wish that it would not.

4200 Campbell Ave., Arlington. $40–$89.(703) 820-9771. signature-theatre.org.