Here’s a historical novel bound to hook you from the start. It’s an exciting read with finely drawn, believable characters caught in a dangerous world.

Set on the Thousand Island headwaters of the St. Lawrence River during the American Civil War, “Grindstone” is a fictional account of the national struggle that affects even those on the sparsely populated northern border. Characters contending with brutality and treachery are as memorable as those in Charles Frazier’s Civil War masterpiece, “Cold Mountain.”

In summary, “Grindstone” by Donna Walsh Inglehart is one powerful book.

Early in the novel we meet the book’s unlikely heroine, an Irish immigrant named Anya O’Neil MacGregor. Like many Irish in the early 1860s, she fled Ireland because of famine and English brutality. She finds work on Grindstone Island on the New York side of the St. Lawrence, where she takes over teaching in a one-room schoolhouse when its male schoolmaster dies fighting with the Union Army.

Not far into the novel, Anya meets young Jonathan Douglas, a former surgeon for the Confederacy who’s hiding out on Grindstone Island. The encounter takes place at Anya’s empty schoolhouse on a snowy evening. Although attracted to each other, they repeat lies that — out of necessity — they’ve spread through the island community.

Anya claims she’s married to a fellow immigrant named Finn who’s off fighting for the Union. Finn is indeed fighting Rebs, but he’s really Anya’s brother. She invented the story to get the schoolmistress job that was closed to single women.

In his deceit, Jonathan says he’s a Union Army minister serving a prisoner-of-war camp on one of the Thousand Islands. In fact, the former surgeon had recently joined a Confederate spy ring whose mission was to torch New York City. But in a final revulsion to war, Jonathan sabotaged the plot. Now he’s hiding from Confederates intent on revenge.

Although confusion sown by the lies is cleared up, Anya and Jonathan remain star-crossed lovers. Anya, contending with poverty and anti-Irish prejudice, cannot openly court Jonathan. He knows he’ll be killed if Confederate agents find him, and fears they’ll slay Anya too.

“He felt such tenderness toward her,” Inglehart writes. “Anya, this Irish girl from a whitewashed village by the sea. For all their differences, they shared a kinship, adrift as they were in this strange land.”

Although “Grindstone” is fiction, there was a Confederate plot to burn New York City by starting fires in hotels. That real-life plot failed, and one Confederate conspirator was arrested and hanged. The New York Times headlined its story on the plot as “One of the most Fiendish and Inhuman Acts Known of Modern Times.”

It’s also true that the Thousand Islands were much affected by the war. Deserters from Union forces hid there to wait out the conflict.

Freed slaves took refuge in the near wilderness, and Confederate spies used the border to plan attacks on northern U.S. cities. Those plans fizzled with surrender.

Inglehart repeatedly visited the Thousand Islands with her husband, a historian with long-standing family ties to the region. Her first novel, a young-reader book called “Breaking the Ring,” was published by Little Brown and Company.

With “Grindstone,” she took a different approach to book distribution.

“I decided,” she said, “to cut to the chase, and published it through a company my husband and I formed, Troubadour Interactive.”

A native of Wayland, Mass., Inglehart came to Maine in the 1970s, where she founded a wilderness summer camp for teenagers.

She graduated from the University of Massachusetts and Middlebury College, and taught English at Northfield Mount Herman School in the Bay State. Today, she chairs the English department at Hebron Academy in Maine.

Critics hail “Grindstone” as “an astonishing piece of historical fiction” with “spellbinding descriptions of the river and islands.” I agree. It’s a gem of a novel.

Lloyd Ferriss is a freelance writer who lives in Richmond.