Sixth-grader Til only rides the ferris wheel on Saturdays, her day with her divorced Pop, but she fears it and comes to see the experience as a metaphor for the helpless terrors of living with her psychotic mother. At first Gertrude seems only superneat and scolding; then we learn that she has seen herself through life as an unloved ""slave,"" and that she resents Til, whom Pop named for a princess (Clotilde). Soon Gertrude is hitting Til around and blaming her for objects broken in the process; and on the night that Til comes home to find the dinner table set with butcher knives, she knows she has to leave. Moeri scores a bullseye with that dinner-table image; and Til's subsequent terrified trip through 1940's San Francisco has enough suspense to pull readers along. Certainly the witch-mother myth that this evokes is a powerful one, but in a realistic story Gertrude is too stridently one-dimensional to be believed, and Moeri's social-worker intentions result in a last-minute rescue that is heaped with messages to the point of ludicrous incredibility.