Playwright Amy Herzog is a member of a three-generation Jewish family in New York  and Boston.  She gained critical acclaim for her 2010 play “After the Revolution,” based on the second marriage of her biological  Grandmother Leepe, who is now 95 and still living in Greenwich Village. Her most recent play, “4000 Miles” is a polished gem of a play that is appearing through Feb. 3 at The Repertory Theatre’s Emerson Studio Theatre. Herzog, who is only 33, demonstrates her outstanding ability to write spot-on dialogue for the two main characters, who are separated by half a century in age and perspectives.

Leo Joseph-Connell, superbly portrayed by Dan McCabe, is a self-described retro-hippie, a slacker without focus or direction in life who lost his best male friend in a freak accident while biking 4,000 miles (hence the title of  the work) from Seattle to New York.

Still reeling from  his loss and fearing a breakup with his girlfriend, and feeling guilty at a too affectionate encounter with his adopted sister, Leo turns up ultra-grungy,  dazed and confused at the Greenwich Village doorstep of his Grandma Vera, who is based directly on playwright Amy Herzog’s actual Grandma Leepe.  Veteran actress Rita Gardner steals every scene without trying to as Vera, who like her real-life counterpart is “very sharp-tongued and quick,  very loving and also very critical,” and “a legendary figure” in Herzog’s real  family.

Vera and her two late husbands were old-time New York lefties, both part of the large group of card carrying members of the Communist Party of the USA from the Great Depression  era of the 1930s.  Back in those days, many Jews gravitated to the Communist Party of Gus Hall or to the democratic Socialists of Eugene Debs and Norman Thomas.  Most later became  mainstream Democrats after FDR launched the New Deal and Joseph Stalin turned off many U.S. Communists by signing the Non-Aggression Hitler-Stalin Pact.

The children and grandchildren of old  line American Communists are called “Red Diaper Babies,” and count among their numbers Amy Herzog, the feminist artist Judy Chicago. the Beat Generation poet Allen Ginsberg and the Watergate partner of Bob Woodward, Carl Bernstein,  among others.  When Leo is challenged about his Communist ancestors by a Chinese American girl he apparently picks up at a bar, he defends their Communism,  saying, “back  then, it was like recycling or  something.”

Vera is physically quite frail and is coping with loss as she lives alone in her spacious,  rent-controlled Greenwich Village Apartment (a special loud shout-out to scenic designer Robert Mark Morgan for replicating the exact look  of actual  Village apartments from that era).  She considers her off-stage, across-the-hall neighbor a “real pain in the ass,”  but values her as a companion, each checking with the other each day to be sure “our toes have not started curling up.”

Jane Page does a superb job directing the small  cast, which includes, besides McCabe and Gardner, Katie McClellan as Bec, Leo’s on-again-off-again-maybe-on-again girl friend Bec, and Lisa Helmi Johanson as Amanda, a fire and brimstone, hedonistic daughter of wealthy Chinese American parents from Taiwan, who absolutely HATE Communists.  Both McClellan and Johanson handle their lines and body language to perfectly evoke their Gen-X and Y generation.

Vera is taken aback  by Leo’s grimy appearance at the start of the play, and like  any good Jewish Grandma, makes sure he takes a shower and lets her launder his sweaty clothes.  In the course of the play, the young man’s energy and youthful ignorance both amuse and enliven Vera, while Vera’s worldly-wise perspectives infuse Leo with a maturity that he has resisted all of his life.

“4000 Miles,” performed over 90 minutes without intermission, leaves the audience wanting more time in the company of Leo and Vera–and eager to see more plays written by the sharp and poignant pen of Amy Herzog.