O’Neill’s brilliant 2002 breakthrough novel, ”At Swim, Two Boys,” swirled history, politics, and sexuality into a raging Irish tempest. ”Kilbrack,” written in 1990 and just now published in America, is more of a teacup — small, warm, and beautifully ornamented — that portends the eventual flowering of a major talent. It begins as the story of a young amnesiac on his way to an Irish village, the subject of a memoir that’s obsessed him. Why amnesia? Why this village? The tragicomic answers make ”Kilbrack” smarter and more haunting than the novel’s minor, mirthful shape suggests.