Riverdale: The Day Before features the perspectives of the four main characters of season 1: Jughead, Archie, Betty, and Veronica. It all takes place the summer before the first episode of season 1. It is a well-written TV tie in. Each character is off on their own, not interacting much with each other. If you have seen season 1, it is easy to pick up on the slight hints on how everything and everyone is connected.
Fans of the show will enjoy getting new insight into the minds of the characters before the show started. You know the outcome but the fun is in seeing how all the characters got to where they ended up. It is also interesting to get inside each character's head and hear their own perspectives on what is going on in their lives. While it does provide enough information for those who haven't seen the TV show, I believe fans of the show will pick up on more throughout the book.
Overall, fans of the show should definitely pick up the book. It will be a fun and enjoyable read.