Boy gets horse. Boy loses horse. Boy (after slogging through the battlefields of World War I) finds horse. The simplicity and sentimentality of this stage adaptation of Michael Morpurgo's children's novel, imported from London's National Theatre, has led a few critics to dismiss it as something less than serious adult theater. But it is childlike in the best sense: narratively clear, emotionally naked and entranced with the visual possibilities of theater. The puppetry (from South Africa's Handspring Puppet Company) behind the incredibly lifelike equine characters is the star of the show. But nearly everything, from the silly little goose that roams the stage on a wheelie, to the low-tech sound-and-light effects that brilliantly re-create the battle scenes, makes this an unforgettable theater experience.