The first 20 sections contain the types of sounds, comparing pairs of sounds in each section. This part is a bit more advanced (or confusing) than the elementary level book of this series, in which the pairs of sounds have the same mouth position (one sound is made by "vibrating" the throat and the other one not). Here you could need the basics presented in the elementary level book. The structure of the book is similar, the exercises are really useful, the audios are appropriate and a little bit more challenging, and the games are quite exciting, they require logic reasoning besides language knowledge.
The emphasis is made in the intonation: 40 sections dedicated exclusively to English intonation. A very good training to deal with the advanced level book of the series.