Mermaids, kidnappers, and mercenaries hijack a tropical vacation in this genre-bending sendup of the American honeymoon. On the grounds of a Caribbean island resort, newlyweds Deb and Chip — our opinionated, skeptical narrator and her cheerful jock husband who’s friendly to a fault — meet a marine biologist who says she’s sighted mermaids in a coral reef. As the resort’s “parent company” swoops...