This book is made up of four stories in four different times in history— one takes place in the stone age, one in thirteenth century England, one in an early 20th century insane asylum, and one in the far future on a rocket ship headed to colonize a new world. The stories all link to each other through spirals, as well as by referencing the other stories. In the preface it said that the stories could be read in any which way, though to make the Goodreads page updates easier on myself I read them in the order they appear in the book.
I loved this book. I thought it was really clever, and the stories were really suspenseful. I liked how each story ended with the character stepping off into the unknown. There were some some minor problems with this book that really bugged me— the first being the cover, which features a picture of a spiral staircase coming out of the waves. Careful inspection reveals that the illustrator (Elizabeth H Clark, in case you follow book jacket artists) just took a section of a spiral staircase and copied it all the way up instead of actually figuring out the correct perspective.
Another was in the final story when the spaceship's computer detects a radio wave signal with a frequency of 1.6180339887 Hz and, because 1.6180339887 is approximately equal to phi (a number associated with the Fibonacci spirals), decides that this is proof of intelligent life. While that number would be significant, the Hz is a completely arbitrary unit equal to one cycle per second, and any alien life sending out such a signal would have no way of knowing what a Hertz is.
Besides that, it was terrific, and now I'm trying to solve the hexadecimal cipher in the back of the book!