Virginia Woolf believed that ordinary decisions matter so much that it's ''very dangerous to live even one day.'' This promising debut novel, a political thriller inspired by Woolf's Mrs. Dalloway, takes that warning literally. Clare Moorhouse is throwing a dinner party to boost her husband's career. But as she prepares, a mistake she made long ago suddenly threatens the safety of everyone near her. Korkeakivi shares Woolf's flair for making everyday rituals (buying flowers, setting the table) seem profound. But too many coincidences in An Unexpected Guest keep her Big Surprising Moments from feeling as meaningful. B

