Jenny O'Hara and Matt Caplan in South Coast Repertory's 2013 production of "4000 Miles" by Amy Herzog. (Debora Robinson / South Coast Repertory / October 23, 2013)

Amy Herzog's captivating character study, "4000 Miles," now on stage at South Coast Repertory, engages its audience early on and maintains that emotional attachment almost to the very end. It's as if the playwright simply had nothing else to say and just stopped writing.

But until that less-than-satisfying conclusion, Herzog's play is a rich and rewarding experience. Director David Emmes has elicited some indelible performances from his four actors, particularly the two central figures — a young man and his nonagenarian grandmother, thrust together for a few weeks in the old lady's spacious Greenwich Village apartment.

These characters, worlds apart in age and viewpoint, are beautifully written and superbly interpreted by Matt Caplan and Jenny O'Hara. Young adventurer Leo (Caplan) has just finished crossing the country on his bicycle and elects to crash temporarily in Vera's (O'Hara) spare bedroom, creating a new form of odd-couple bonding.

During this visit, Leo interacts with an old girlfriend on her way out (Rebecca Mozo) and a new one on her way in (Klarissa Mesee). But the crux of this dramatic comedy is the relationship between the young, athletic Leo and the aging, absent-minded Vera and how they affect each other's life.

O'Hara enriches her portrayal with age-defining mannerisms, all well chosen and highly believable. Age has dulled her 91-year-old character's memory, and she frequently employs the term "whaddayacallit" to describe something for which she's mentally lost the word. Her performance is wonderfully nuanced, a convincing blend of warmth and scrappiness.

As the grandson, who has lost his best friend on the bike trip in a horrific accident and now must face life without his lady love, Caplan delivers a performance layered with degrees of emotional intensity. We view the play chiefly through his eyes and feel his several degrees of pain and loss as he attempts to forge a new path.

Mozo's brief appearance to sever the relationship and her late return to salve the wounds constitute a heartwarming depiction by this frequent SCR performer. Mesee, on the other hand, delves heavily into comic relief as a chirpy, kooky Chinese girl brought back to the apartment by Leo for an intended tryst.

That apartment, incidentally, is quite huge, judging by the extra-large living room and other, unseen quarters. Scenic designer Ralph Funicello has fashioned a richly detailed setting that appears to have been around as long as its owner.

Sara Ryung Clement's finely detailed costumes (especially Mesee's colorful garb) and the sharp lighting effects by Lonnie Rafael Alcaraz complete a splendid atmospheric picture.

The structural flaw materializes in the play's last few minutes when the focus turns to an unseen, and only casually mentioned, character whose demise alters the course of the action. Herzog is a talented and perceptive playwright, and her character depiction is first-rate, with the exception of that fizzled finale, resulting in the lack of a resolution. With some detailed work on that aspect, this could be a superb effort.

Up to the closing moments, "4000 Miles" is a truly engrossing production, calculated to involve its audience in this otherwise impressive engagement at South Coast Repertory.

TOM TITUS reviews local theater for the Daily Pilot.

If You Go

What: "4000 Miles"

Where: South Coast Repertory, Segerstrom Stage, 655 Town Center Drive, Costa Mesa

When: 7:30 p.m. Sundays, Tuesdays and Wednesdays, 8 p.m. Thursdays through Saturdays, 2:30 p.m. Saturdays and Sundays until Nov. 17

Cost: Tickets start at $22

Information: (714) 708-5555 or http://www.scr.orghttp://www.scr.org