In this book Vonnegut presents caricatures of religion, the hubris of scientists, and the dangers of technology. Jonah, the storyteller of "Cat's Cradle", is writing a book about what some people were doing when the atom bomb was dropped on Hiroshima. He focuses on the eccentric Dr. Felix Hoenikker - "father of the atomic bomb" - and his three children.
He's told that Dr. Hoenikker was playing "Cat's Cradle" with a piece of string when the bomb went off. Jonah also learns that, when the Marines asked Dr. Hoenikker to 'do something' about mud (which was difficult to wade through while fighting), he invented a substance called Ice-Nine - which causes water to instantly crystallize and harden. Moreover, the effect rapidly spreads, solidifying all water far and wide - a very dangerous phenomenon.
Upon Dr. Hoenikker's death his children divide his stockpile of Ice-Nine to safeguard it. The children then go their own way. After a time, Frank, the oldest child, becomes the assistant of the President of a Caribbean island called San Lorenzo. When Frank plans to marry, his sister Angela and his brother Newt - along with Jonah - travel to the island to attend the wedding.
Jonah finds that San Lorenzo is a very odd place whose residents practice a forbidden religion called Bokononism, which has some strange customs (e.g. people press their feet together in lieu of sex). He also discovers that each of the siblings has given away a bit of their Ice-Nine to garner some advantage for themselves. With Ice-Nine on the loose all over the place can disaster be far behind?
The book has an eclectic variety of weird, often funny, characters involved in a mildly engaging story.