One evening, Cleveland Heep, who became the superintendent of a Philadelphia apartment complex after his family was murdered, discovers Story, a Narf (a naiad-like being) from the Blue World, in his building's pool, immediately rescuing her from an attack by a Scrunt, a grass-covered, wolf-like creature that hides by flattening its body against the turf.
Story explains she is a Narf, here to find the Writer, the "vessel" who will be magically awakened when he meets her, and then write a book that will save humanity in the future. When Heep mentions the word Narf to tenant Young-Soon, she recognizes it from stories told by her mother, Mrs. Choi, then expands on for him.
After questioning residents Farber, Bell, Dury, and five nameless smokers, Heep discovers the Writer is tenant Vick Ran, who is struggling to complete The Cookbook. Heep brings Vick to Story, which eliminates his fear and sharpens his inner voice. She later reveals that The Cookbook will contain views and ideas so significant they will inspire a future President, a great Midwestern orator, to greatly change the world for the better. Vick later deduces, and she confirms, that he will be assassinated because of the controversial nature of his ideas, giving them extra power.
As Mrs. Choi remembers more details of the Narf legend, Heep better understands the situation. The Tartutic, an invincible simian-like quartet that serve as the Blue World's peacekeepers, have forbidden any attacks on Story while she returns home. Nonetheless, the Scrunt does just that because they know that Story is destined to be a great Narf leader. To recover from her wounds and return safely, she will now need the help of a Guardian, a Symbolist, a Guild, and a Healer. Story believes Heep to be her Guardian; Heep asks Farber, an abrasive film critic, to help him figure out the others' identities. Working off movie tropes, Farber misadvises Heep, leading him to a flawed conclusion that Dury is the Symbolist, the smokers are the Guild, and Bell is the Healer.
Heep confronts the Scrunt, but nearly dies in the process, convincing him he is not the Guardian. The next night, Farber's bad advice leads to their plan's immediate failure. In the confusion, Farber is killed and Story is mortally wounded by the Scrunt. Dury suddenly realizes his son Joey is the real Symbolist. Interpreting the information on cereal boxes, Joey deduces the true Guild is composed of seven sisters, that two new men must be present, and that the Healer is male, soon revealed to be Heep. Heep goes about healing Story by "bringing forth [his] energy" (his repressed grief), and Story's wounds heal when he confesses that he does not want to lose her too. Story's departure starts again, but the Scrunt attacks; it is stopped by the gaze of Reggie, a lopsidedly muscled tenant who is the true Guardian. Reggie's intense stare and stalking approach compel the Scrunt to slowly retreat, but he is distracted by the cry of the Great Eatlon (a giant eagle who will ferry Story home). When Reggie breaks eye contact, the Scrunt leaps, but the Tartutic arrive and drag it away. Heep thanks Story for saving his life as she hugs him goodbye. The Great Eatlon lands, enfolds Story in one of its wings, and takes flight, ferrying Story into the night.
Paul Giamatti as Cleveland Heep
Bryce Dallas Howard as Story
Bob Balaban as Harry Farber
Jeffrey Wright as Mr. Dury
Sarita Choudhury as Anna Ran
Cindy Cheung as Young-Soon Choi
Freddy Rodriguez as Reggie
Bill Irwin as Mr. Leeds
Jared Harris as Goatee Smoker
Mary Beth Hurt as Mrs. Bell
Joseph D. Reitman as Long Haired Smoker
Tovah Feldshuh as Mrs. Bubchik
M. Night Shyamalan as Vick Ran
Noah Gray-Cabey as Joey Dury
June Kyoko Lu as Mrs. Choi
David Ogden Stiers is the uncredited narrator heard at the opening of the film, explaining how: the magical Narf of the undersea Blue World provided guidance to humanity millennia ago; humanity has forgotten that relationship, plunging itself into the devastating wars that are referenced through the remainder of the film; seeing the looming end of humanity, the Narf have now sent some of their (human-appearing) young to help humanity, though most are killed by the Scrunts and humanity has forgotten how to listen to the others.