Translation:It is a book about hot nights and cold mornings.
The whole lesson was like a story about a one-night stand LOL They had a great night, but she wasn't happy in the morning, he wants to talk about it, she doesn't want to...
Seriously, I thought I must've been totally off with the translation - wonder what inspired the sentence? >_>
I think I can answer this one... "to" can't be paired with "kniha" because they don't agree on gender, so it can't mean "the", it has to mean "it"
I presume he means "It is THE book about..." instead of "It is A book about..." And since Czech has no articles, unless "je to" is only used in a sentence which, when translated to English, would use the indefinite article (which I doubt), both translations should be correct.
What you're probably getting at is "Je TA kniha o..." (this word order would be a question), or "TA kniha je o...", which would be a demonstrative, and as such would most likely be translated to English as "that", but I guess "the" could work too.
the situations in which the english version works with the definite article would also call for the demonstrative "ta" in czech: Je to ta kniha o...