Most people in the town of Rivershore, Michigan view Mary Harrington as a quiet widow whose only oddity is that she spends a lot of time at the gym. Her son thinks it’s time for her to move into a retirement home. Two gang members think she’ll be an easy target. No one in Rivershore knows what Mary did in her younger years—really did—but the two gang members discover they’ve underestimated their victim . . . and Mary fears reverting to old habits may have jeopardized her future.