BOOK SIX in the series: Apparently of its own volition, an antique crossbow, long perched high on the wall of the great room in Winston Rafferty's Mansion, fires and kills one of the guests at a publisher's book launching party. There are a variety of suspects: the publisher, three mystery writers, a universally disliked book critic, the cantankerous neighbor and his son, the wily old grounds keeper, the maid, and the new assistant to Rafferty