Essentially it's a prequel to the series and is set during the summer before they start at Roundview. It's easy to read with the narration switching between the various characters, frequently in a single scene which makes it easy to put down and pick up again.
It fills in some of the background of the characters but doesn't give away any major secrets though it does explain more clearly some of the motivations of some of them. Nick, for example, comes over as a nicer and less superficial person than you might imagine. We find out that Grace has just joined old friends of Mini and Liv shortly before the start of the book and is still getting to know them rather than them being a tight threesome as it first seemed in the opening episode of the new series. They also know who Alo and Rich are. Matty doesn't appear at all but we do find out what triggers Frankie's move to Bristol. Some other characters are introduced with one in particular whom it would be good to see in the next series. This is Rhodie, a likeable deaf girl who doesn't speak, and who makes Alo's few days in Newquay very memorable.
This is a light and quite aimiable read, pretty much like Season 5 as a whole really, so if you liked that then...