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 in to corner the market on mythological creatures, the couple joins forces with other adventurous souls, including an ex-Navy SEAL with a love of explosives and a hipster Tokyo VJ, to save said mermaids from the "Venture of Marvels," which wants to turn their reef into a theme park.

Mermaids in...