Intriguing start - how will this puzzle fit together?

In the books prologue, Mariana knows with certainty that Edward Fosca is a murderer. We don't yet have any idea who he is, but Mariana knows with every cell of her body that he's guilty of killing at least two people. Mariana is determined to outsmart him and catch him. Mariana is a brilliant group therapist who grew up in Greece. She lost her mother at a young age and grew up with a cold, distant father. She is mourning the loss of her husband Sebastian while proceeding with her group therapy sessions. The first look is off to a puzzling but strong start. It's clear this book is going to be a mystery - who was murdered? How does Mariana know with such certainty that Edward Fosca is the guilty party? We have a few starting pieces to the puzzle, but no idea yet of how they're going to fit together. It is interesting and compelling - I absolutely want to read more and hear what happens next.