The cast of The Mystery of Love and Sex at Signature Theatre. Photo: Margot Schulman

It’s hard not to fall for each of the funny, flawed people at the center of Bathsheba Doran’s The Mystery of Love & Sex, now playing at Signature Theater. Doran has a knack for imperfect, human characters that radiate and resonate, and director Stella Powell-Jones has found the precise cast to bring them to life.

At first it’s puzzling why soulmates-on-paper Charlotte (Shayna Blass) and Jonny (Xavier Scott Evans) seem to be together, but not exactly dating. Best friends since childhood, they’re found in the first scene putting together a makeshift family meal for Charlotte’s visiting parents (“Bohemian!”, her mother Lucinda declares it — more than once), and there’s talk of living together and marriage. But as the story continues, the picture painted of their sexuality and experience becomes more complex . Much of The Mystery of Love & Sex is spent tenderly watching them figure it out, shifting the audience almost unwittingly into detective mode in the process (perhaps intentionally — Charlotte’s father is, in fact, a writer of popular detective fiction).

Though a portrait of this pair, as well as Charlotte’s well-meaning, meddling parents (Emily Townley and Jeff Still), The Mystery of Love & Sex smartly captures bigger themes like subtle racism and the kind of inner havoc stricter religions can wreak on the conscience. Doran’s script is rapid-fire and funny (“You can get fat and pretend it’s a political statement,” Jonny comforts Charlotte in one scene), though it takes a polemic turn in the second act.

Each performer is well-suited to his or her role. It’s satisfying to see Evans transform from awkward college student to a man increasingly comfortable in his own skin. Blass sells Charlotte’s complications without ever shifting into caricature, and Townley has whip-smart timing tossing Lucinda’s barbs, while still retaining her warmth and acceptance. Jeff Still has the showiest role in Howard, Charlotte’s complicated and commanding father, and he brings charm even during Howard’s most maddening moments.

James Kronzer’s set does a good job capturing the action in tight spaces, widening things up during a couple pivotal scenes in the family’s tire swing-centric backyard. It is there where the story’s tone shifts back to a wacky and warm family comedy. It might take a few expected emotional turns to get there, but the audience begins and leaves with raw affection for this quirky quartet.

The Mystery of Love & Sex runs through May 8 at Signature Theatre. Tickets ($40-89) are available online.