This book is almost perfect,
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This review is from: The Cucumber Book: Behaviour-Driven Development for Testers and Developers (Pragmatic Programmers) (Kindle Edition)
The net result of reading this book is that you feel like you've used the technology and understand why it is the way it is. I would have preferred a bit more emphasis on patterns and for there to be a section on the now more standard Cucumber JVM-based approach. However, this book is still eminently readable and understandable, even to non-Ruby experts.
One of the authors is the guy who came up with the idea. You can't get a more authoritative source.