The Bigtree alligator wrestling dynasty is in decline. And Swamplandia!, the family's island home and theme park, in the Florida Everglades, has sophisticated competition - The World of Darkness. Ava is a resourceful, but terrified twelve-year-old, who must manage seventy gators, and the vast landscape of her grief. Her mother, Swamplandia!'s star attraction, has just died; her sister is having an affair with a ghost called the Dredgeman; her Grandpa has been sent to an old folk's home; her brother has defected to The World of Darkness to keep the family afloat; and her father is AWOL. To save them, 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.