The humans' journeys include both mystical transformations of their bodies and trips to worlds that parodied famous fantasy novel locales.

The book's title is an homage to "Sit Down, You're Rockin' the Boat", a song written by musical theatre composer-lyricist Frank Loesser for Guys and Dolls, in which the character Nicely-Nicely Johnson, making a gospel style confession at a Salvation Army prayer meeting, tells of a dream in which his fellow passengers, on a "little boat to heaven", warn him that if he upsets the ride, he will be washed overboard: "and the Devil will drag you under/By the sharp lapel of your checkered coat...".

As catastrophic natural disasters envelop the world, Mac Walters and Jill McCulloch find themselves in Reno, Nevada.

Entering a nearby bar, they encounter a demon named Asmodeus Mogart, who tells them that Earth is but one of thousands of universes set up by the mysterious Department of Probabilities, and that he can save the world if he can gather six magic jewels.

Walters and McCulloch are able to defeat Mogart, however, and the Department of Probabilities chooses them to jointly guard Earth against further trouble.