This steady, sober hostage story is not quite a thriller, as it isn't played for maximum suspense, yet isn't a full-bodied novel either. About all we know about 17-year-old Doll's boyfriend, for example, is that he is there--on the outside somewhere--and is the son of one of the other hostages. Like a good many British mysteries, what this does give you straight off is an extensive, middle-class novel's sense of the immediate milieu and occasion. Here the event is the latest in an annual series of original operas, produced at their fairly upper-crust neighborhood church by a handful of adults (the ""opera malta"") and the child performers they select. Doll, now too old to perform but devoted to the opera, has wormed herself in as a sort of all-round assistant to the mafia, which includes her talented cellist mother. (Though Mum still plays here and there, she gave up a probable top-rank career on Doll's probably accidental birth.) Every year the mafia's limit of 100 children is stretched to accommodate the clamor for parts, and this year, despite early resolve, Doll's father (he's in government) persuades them to admit a hundred-and-first: Juan O'Grady, the son of the ambassador from the oppressive South American country of Matteo. (This favor for the relatively moderate-leaning ambassador might boost prospects for British pressure on human rights issues.) Rehearsals absorb everyone--Doll loves it all--but on dress rehearsal day four Mattean revolutionaries, attempting to kidnap Juan, shoot his bodyguard outside and end up in the church with the whole cast and opera mafia on their ill-prepared hands. Though arrogant Juan has not been popular, all conspire beautifully to hide him, but he is finally discovered during a gun-point command performance. One of the ""bandits,"" a former teacher, speaks simplistically but effectively of conditions in Matteo, and in the end Doll's apolitical, abstracted Mum, a stand-in for them all, is put on trial for fiddling, as it were, while Matteans die. A liberal mafia member who opposed admitting Juan and has previously forwarded these same arguments now speaks as defense attorney in favor of art, its validity, and its free pursuit--but after the ordeal is over the hostages are ""terribly sympathetic to the bandits"" and Mum is talking about selling her prized and valuable cello. You have to be willing to hear a lot about the workings of the opera (and little else) to stick with the first 70 small-print pages; and the moral-philosophical argument that dominates later pages is more earnest than original. But anyone with a matching earnest receptivity can be engaged by the argument and enveloped in Dickinson's carefully textured citadel.