Writers have a long-running debate over the question of whether to prologue or not to prologue (if I may twist Shakespeare and turn a noun into a verb). Some readers skip prologues. After all, it's asking a lot of a reader to invest mental energy in imagining a world and getting to know characters who then vanish after a few pages, possibly never to reappear. But prologues, like any other writing tool, can work sometimes.
I think prologues should be careful not to tip the
writer's hand too far. The prologue shouldn't introduce the very piece
of information that the main character will spend a whole book seeking:
the identity of the jewel thief; the answer to
what's-in-the-mystery-box; the truth about where the MC came from. Those
mysteries can be hinted at, but if they're completely solved in the
prologue, then we have little motivation to read on. It's no fun waiting
too long for a main character to catch up with us.
A good test
for a prologue is this: If I cut it out altogether, does the book hold
together? Actually, that's a good test for the necessity of any chapter,