In Harry Cauley's novle, Millersburg, cantankerous Mamu rules her Millersburg, N.J., farm family, including 17-year- old narrator and grandson Ben, with an iron fist. She builds resentment with a sharp, truthful bite, telling her daughter, ''You were a mistake.'' A double murder linked to Mamu's brother Josh undoes the rigid peace, forcing the clan to abandon its unspoken rules, open up, and implode. In this judiciously short read, Cauley develops his characters with slow control. Mamu may seem cold at first, but it's a ruse Mamu finally reveals her vulnerability in a shocking revelation to Ben. When the family members' various secrets come out, you can't help but sympathize with them, even hapless Mamu.