Avidly, Gemma and Andrew pore over the extraordinary manuscript forced on him by a passing hen: ``The True Story of Harrowing Farm.'' The hen tells how little green men shoo her and her fellows from the cramped cages where they've been confined to lay eggs, uncomfortably, in public, then fit the cages to humans- -the species they prefer as food. Horrified to see people suffering as she used to, the hen stows away on the men's spaceship and becomes a TV celebrity on their planet, successfully pitching her plea: no one should eat an animal that isn't first allowed a happy life; anyway, grains and vegetables are more efficient foods. The message dominates; but Fine (My War with Goggle-Eyes, 1989) is an imaginative humorist who treats the gruesome reversal with a light touch. The satirical episodes of the hen's space adventure alternate with the kids' responses to it (incredulous, then concerned); meanwhile, Fine points out how humans keep uncomfortable truths (like conditions in chicken factories) concealed. Animal-rights advocates will be delighted; others can enjoy Fine's wry wit—and have their sensitivities enhanced. (Fiction. 8-12)