“I Do! I Do!” covers 50 roller-coaster years of a marriage, with young performers playing the couple and a pianist laying the foundation.

Of note, the musical was created by the same team who made the famous “The Fantasticks,” Tom Jones (words) and Harvey Schmidt (music).

The show’s best-known song is “My Cup Runneth Over,” a beautiful picture of time-tested marital love. In this production, it is set up so well that to applaud afterward would break a spell.

The song finds Justin Winterhalter and Melanie Joy Hall at their best. They ooze warmth and tenderness.

Direction and choreography by James A. Zimmerman and piano accompaniment by Cornell Blanchard more than casually assist in this.

“I Do! I Do!” arrived in 1966 as a kind of oasis in the turmoil of the Vietnam War. The show looks back to 1898 and into a bedroom (brightly presented) of a what-might-have-been marriage.

The couple is somewhat well off. He’s a writer, able to support a wife, two children, an ample house and a servant.

What the show says to today’s couples is not clear — except maybe that marriage of any era is not easy all the time.

The man (Michael) complicates his with a huge ego. That a writer would have one is pure fiction. (That’s a joke). Michael has flashes that make him distasteful.

The script nips at Agnes, his wife, for spending too much and being late. Otherwise, she’s the glue of the relationship. She can withstand Michael’s one-time wandering eye.

In a key scene, Winterhalter uncorks the strutting “It’s a Well Known Fact,” about how men age gloriously while women go to pot. Hall answers with “Flaming Agnes,” a hotsy-totsy tune about how much fun Agnes could have as a liberated woman.

Winterhalter and Hall are appealing. They shape the characters and story well. Body microphones help their voices carry. What they don’t have is the kind of voices that can always hold a long note without drifting from that note.