I'm revising my WIP. In the rough draft, I started with the characters going on an adventure. Most of what happens in the first chapter of the book is in response to a murder, but there is no who-done-it. It's not a mystery. I feel like the story would benefit a lot from a 2-3 page prologue. I could start it with action, explain the most important aspect of the magic system, provide context for the culture so that the reasons for the murder are understood, and create sympathy for the killers all in one go with very little telling and no info dumping. I'm hesitant to call it "chapter 1" because the killer is only in one other scene in the whole novel, and it is so short. What do you think?