In the Upper Country by Kai Thomas

The fates of two unforgettable women—one just beginning a journey of reckoning and self-discovery and the other completing her life's last vital act—intertwine in this sweeping, deeply researched debut set in the Black communities of Ontario that were the last stop on the Underground Railroad.
Young Lensinda Martin is a protegee of a crusading Black journalist in mid-18th century southwestern Ontario, finding a home in a community founded by refugees from the slave-owning states of the American south—whose agents do not always stay on their side of the border.

One night, a neighbouring farmer summons Lensinda after a slave hunter is shot dead on his land by an old woman recently arrived via the Underground Railroad. When the old woman, whose name is Cash, refuses to flee before the authorities arrive, the farmer urges Lensinda to gather testimony from her before Cash is condemned.

But Cash doesn't want to confess. Instead...