The only teenager left on Kinnan is Eilidh (played by the energetic Lois Craig), whose daily routine of lonely distance learning (no teacher remains on the island) is interrupted when she finds a dying whale calf on the shore. The next day, a young woman named Arran (Stephanie MacGaraidh) washes up. Her curious stories remind Eilidh of her home’s surreal folklore — that tensions once literally split Kinnan into two islands, dividing the farmfolk, who stayed, and the fisherfolk, who moved to a mist-shrouded land to become whale herders.

As the two main characters’ friendship unfurls and parallel lives intertwine, the Scottish actresses arrange their golden voices into swooping, haunting harmonies that fill Olney Theatre Center’s main stage, aided by sound designer Sam Kusnetz, with a blend of folk, pop and electronica, further bridging the contemporary and the traditional. That’s a signature of lyricist and musical director Finn Anderson, whose other works, too, deal in enchanting folklore.

Craig and MacGaraidh also take on the roles of the townspeople, each about 10 characters total, including a marine biologist, a retiree in search of his lost garden gnome and Eilidh’s mischievous but aging gran. They’ve received an offer from the government to relocate to the Scottish mainland, and assemble at a town hall (or a “spikkin,” as Eilidh’s grandmother reminds her to call it) to discuss whether to accept the offer. Some, like the nine-months-pregnant Breagha, are torn between a desire to stay and the reality that the island is well toward extinction, with no doctor and a last struggling farm.

It would be easy for the constant role-switching to become tiresome or confusing, but Craig and MacGaraidh handle it with a nimble grace. (Because these parts are so demanding, Sylvie Stenson and Julia Murray rotate in as performers.) It’s exciting to watch them jump between characters, molding their limbs, pitching or deepening their voices, taking on slouches and scowls and sighs, with such dexterity, often between lyrics.

“Islander” was conceived by Amy Draper around 2017 and made a splash at the 2019 Edinburgh Fringe Festival before moving to an off-Broadway run and eventually embarking on its current North American and European tour. Its most visible theme — the grim fight to hold on to a thin slice of home on a planet threatened by a changing climate — speaks more forcefully now, perhaps, than when the musical was initially developed. But in a smaller, more specific way, “Islander” is also about the little acts of care and kindness we show each other and a wholehearted belief in the power of community.

That’s why, when Eilidh and Arran part, their bittersweet vow to reunite rings oddly hopeful. “If the whales are still swimming,” Arran says.

“If we’re still here,” Eilidh replies.

Islander, through April 28 at Olney Theatre Center in Olney, Md. 90 minutes, no intermission. olneytheatre.org.