I have been offered to review a book. It is written by one author only (it is not a collective work) and effectively it is divided into three parts, which are on the same field, but deal with completely different topics and are not that connected to each other. I am more interested (and specialise) in part 2. Do I only review only this part, only briefly mentioning the other parts? Or I have to review all parts equally? What do you think? The review must be under 1500 words.