The heroes—and anti-heroes—of I Am an Executioner include a misunderstood tiger whose affection for his keeper goes horribly awry, a woman trying to celebrate Thanksgiving with her husband’s corpse sprawled on their living-room floor, and an ex-CompUSA employee setting up a medical practice armed only library books and fake business cards. Rajesh Parameswaran has a riotous, singular imagination that promises to dazzle the universe of American fiction.