The book appears to be formatted with the <pre> tag instead of <p>. The default for <pre> is to use a monospaced font, and to preserve whitespace.
As well as removing the font-family:monospace and white-space: pre-wrap properties, you could try adding something like this to the stylesheet:
Code:
pre { font-family: inherit; white-space: normal; }
but the <pre> tag is likely to mess up the formatting options on some ereaders, so a real fix would probably involve replacing all the <pre> tags with <p>.