For nearly 50 years, readers have expected fictional experimentation from the acclaimed Hawkes (The Frogs). In his amusing, slight 17th novel, however, the experiment takes an indistinct shape--a bit of a myth, a children's story, a farce (with the ""Irishness"" of the title posed in a sardonic wink). The story concerns young Irish foundling Dervla ""Thistle"" O'Shannon, who narrates the curious sequence of events that befall her during her 13th year. The action starts on an orphanage visit to the neighboring Old Soldiers' Home, where Dervla befriends Corporal Stack, a WWI veteran several generations her senior. Together, they leave their homes, embarking on a curious courtship that soon finds the Corporal injured and both of them kidnapped and held captive in a declining Great Manor by a young mistress, her brother and a litter of desolate babies. Things only become stranger. The highlights of the story are the apocryphal letters Dervla writes to the head of the orphanage. Supposedly recounting her visit to the Corporal's family, they combine an Irish fairy tale with her own clever reimagining of her situation. Also wonderful are the delirious scenes in which Dervla meets the Corporal (scarily disguised in his old gas mask) or discovers her mistress's brother in a drunken, nauseated stupor. Unfortunately, these most vivid moments of the book exude a drama that neither the characters nor their far-fetched story seems designed to sustain. (Sept.) FYI: A film version of Hawkes's The Blood Oranges will appear this fall, simultaneous with new editions of The Blood Oranges and The Frog.