“Summer Friends” marks the ninth novel from warmly regarded Portland writer Holly Chamberlin, and, as you might expect, the experience shows. This time, Chamberlin gives us more than a seasonal story of Maine’s beautiful southern coast. “Summer Friends” tells an insightful story about people and the different social environments in which they choose to spend their lives.

Most of all, however, this novel takes a long and thoughtful look at individuals shaped over the years by Maine’s salt air and seacoast — who they are inside and who they appear to be in their relationships with families, lovers, friends and the larger outside world.

That’s a complex laundry list to set forth for any novel. Yet, by and large, Chamberlin does it justice. As the title implies, “Summer Friends” follows the lives of two young girls — Delphine Crandall and Maggie Weldon — the first deeply rooted in Maine, the second at home in a wealthy family “from away” (although not all that far away; in this case, Maggie comes from Massachusetts). The two become best friends as 9-year-olds during an idyllic summer in Ogunquit.

How will that friendship fare as they age and change over the next 20 years? That’s the question “Summer Friends” sets out to explore. And the exploration uncovers hidden depths.

Chamberlin taps into the tensions that intrude and shape friendship over time. Delphine and Maggie may start their journey of friendship together, more alike than different, but they soon embark on different life paths. In their formative years, which extend through college in Boston, much remains the same. But Delphine, after a compelling romance with a campus leader, changes course and, after graduation, moves directly back to Ogunquit to help her family with its farming and food enterprises there.

Like the mystic island of Brigadoon, the different world of Boston — with her fiance, her best friend and all they have meant to her — disappear from her life.

Maggie, by contrast, builds a career in the city, becoming a successful financier. She marries a successful lawyer, has two children and settles in the comforts of an upscale suburban lifestyle in Lexington. Delphine slips out of her life.

And so it goes for 20 years until Maggie, sensitive and alert to change, decides to return to Ogunquit to revisit her childhood friend and bridge the distance the years have created. It’s no easy task, and Chamberlin deftly tackles the tension and suspense.

There is a palpable sense of real life in the developments that follow. The two women at the center of this enjoyable novel are not cardboard heroines who can be pushed into contrived scenes on a sunlit summer stage. They are, thankfully, real women who have made real choices and are assessing those choices at a time of their life when their AARP cards are in the mail.

The result is a novel rich in drama and insights into what factors bring people together and, just as fatefully, tear them apart.

All of that is very much to the good. At the same time, there are opportunities in the novel I was sorry to see left largely under-explored.

Chamberlin creates around the central figure of Delphine a large and lively family working together to harvest a living out of their farming enterprise in Ogunquit. They are a salt-of-the-earth Maine family with deep and traceable roots in their community. As such, it seems to me, they were offered as people to be treated with respect, even admired.

At the apex of this family, however, stands Delphine’s mother, Patrice, who seems to squelch every opportunity for a different kind of life for Delphine and to resent every momentary joy in her daughter’s life.

For her part, Delphine acknowledges she often feels unappreciated and undervalued. I agree with her. I can think of no excuse a family can reasonably offer for refusing to travel a brief 60 minutes to Boston to attend the college graduation of a daughter who has spent four years striving for achievement. Yet that happens here. And it is inexcusable. Pride of place is one thing; mindless insularity is another. And insularity wields the trump cards here.

As our heroines learn, sometimes running away is just that — running away — even when a person is running home. “Summer Friends” offers hope of a better way.

Nancy Grape writes book reviews for the Maine Sunday Telegram.