The Bigtree alligator wrestling dynasty is in decline—think Buddenbrooks set in the Florida Everglades—and Swamplandia!, their island home and gator-wrestling theme park, is swiftly being encroached upon by a sophisticated competitor known as the "World of Darkness."

Ava, a resourceful but terrified twelve-year-old, must manage seventy gators and the vast, inscrutable landscape of her own grief. Her mother, Swamplandia!’s legendary headliner, has just died; her sister is having an affair with a ghost called the Dredgeman; her brother has secretly defected to the World of Darkness in a last-ditch effort to keep their sinking family afloat; and her father, Chief Bigtree, is AWOL. To save her family, Ava must journey on her own to a perilous part of the swamp called the "Underworld," a harrowing odyssey from which she emerges a true heroine.