With its inspired counterpointing of Homeric and Caribbean themes, Derek Walcott's new play, commissioned by Britain's Royal Shakespeare Company, springs from the same imaginative sources as his epic poem "Omeros." Episodes of the story of Odysseus' protracted wanderings from fallen Troy to his island home of Ithaca are pungently interspersed with a commentary by the blind singer Billy Blue. Proteus, the Old Man of the Sea, the giant Cyclops, Circe and her revellers, ghosts, and mermaids are among the cast. With its vast sweep and richly figurative language, "The Odyssey "confirms that Derek Walcott is as compelling a playwright as he is a poet.