A scruffy assortment of north country teenagers camping out in an abandoned mill are trapped inside by the tougher, and better armed, Bullman Lane gang and fred themselves sharing their siege with two city-bred hitchhikers who are not only incongruously middleclass but hopelessly ""old"" (about twenty). The boys' reluctant alliance with their accidental guests seems to presage one of those ""realistic adventures"" strewn with class cliches, but Annabel Farjeon, a newly surfaced member of ""the well-known writing family,"" gets the respective accents just right, keeps the suspense taut and shows the boys to be much more than their hard-luck circumstances (and the bleak futures they face with the imminent end of their school careers) would suggest. The group's leader is Polak, a tough kid with a streak of magic, who rather enjoys their dangerous predicament, can summon up tragic tales of revenging witches from his Polish childhood and has inherited a talent for acrobatics from his dancer father. The superficially stoical Polak is a perfect foil for his pals -- particularly George, an inveterate scribbler with newspaper ambitions, and the gentle, cherubic Es. During two days of siege, Polak leads several attempts to break through to the village for food, engineers the removal to a hospital of the hitchhiker Christopher, whose leg has been broken in a run-in with a Bullman Lane raider, and forms a wordless but mutual infatuation for Christopher's sleek sister Lucy. But the most notable thing about Polak is the grace with which he wears his role as an instinctive outsider in company that's up to the demands of their tight situation if not quite his equals in spirit.