IN HIS EXCELLENT ESSAY, “Parvenucracy,” about that most addictive of TV series, Downton Abbey, Alexander Chee makes this provocative statement: “all historical fictions are ruses — to succeed, they all flash a bit of what Genet would call the garter, the anachronism that tells you it’s not real — this is what engages the audience.” In Downton Abbey, the “garter” is the continuance of the estate and Lord Grantham’s way of life within it: these things would never exist if it weren’t for Lady Grantham’s fortune. Lord Grantham, Chee argues, is actually the director of a theatre piece for the benefit of Lady Grantham. This is the way things used to be, his life says, wasn’t it grand? And Lady Grantham, charmed by her lord’s nostalgia project, keeps him in cash. Equally charmed, we do the same for the production staff and all the good people at Masterpiece Theater.

In Caleb’s Crossing, the garter is the narrator herself, Bethia Mayfield. Bethia is the daughter of a Puritan missionary and granddaughter of the founder of a colony of “English” living in a settlement called Great Harbor on “the island” (an early Martha’s Vineyard). Bethia sets her story down in a “spiritual diary” on scraps of paper she’s stolen from her brother, Makepeace, and she divides her narrative in three sections. The first, set in 1660 when Bethia is 15, tells how Caleb Cheeshahteaumauk, a Wampanoag Indian and nephew of the tribe’s great shaman or pawaaw, came to study Christian thought and classical languages and literature with her father at the Mayfield house. The second, set in 1661, tells of their journey from Great Harbor to Cambridge, where Caleb and Makepeace continue their studies at Master Corlett’s grammar school and then move on to “the college” (an early Harvard). And the third jumps to 1715, when Bethia is an old woman on her deathbed, and brings the story of Caleb’s crossing — from the island to the mainland, and from one culture to another — to a tragic close. Brooks is a meticulous researcher, and Bethia’s voice is full of tantalizing colonial-era words — haggering, fanfarroons, sonquem, wetu — all of which help bulk out the illusion that the mind we’re engaging with is really a creature of its time. Brooks’s language is carefully laid down. Here’s one of many delicious passages, this one coming early in the book, when Bethia is reflecting on her girlhood:

Those hot, salt-scoured afternoons when the shore curved away in its long glistening arc toward the distant bluffs. The leaf-dappled, loamy mornings in the cool bottoms, where I picked the sky-colored berries and felt each one burst, sweet and juicy, in my mouth. I made this island mine, mile by mile, from the soft, oozing clay of the rainbow cliffs to the rough chill of the granite boulders that rise abruptly in the fields, thwarting the plough, shading the sheep. I love the fogs that wreathe us all in milky veils, and the winds that moan and keen in the chimney piece at night. Even when the wrack line is crusted with salty ice and the ways through the woods crunch under my clogs, I drink the cold air in the low blue gleam that sparkles on the snow.

For anyone who’s ever spent any time on Martha&...