Dear Plotting Author…
The unknown fate could be cool. Try it! Your awareness of potential irritation means you’ll strive for a story that nails “enthralling.” I have two recommendations for your proposed structure: 1) Keep Victim present in Book 2. Not physically, but through Driver’s story. Perhaps this is a small town and after the crash Driver encounters people that readers met in Book 1. These people are doing business that somehow relates to Victim, none knowing Victim was in an accident. Perhaps Driver discovers a link to Victim, or a hint as to Victim’s identity. The point is to make Book 2 as much about Victim as it is about Driver. Don’t abandon Victim yourself. Keep her with us and even advance her story, building readers’ desire for her rescue beyond basic justice. Then the unknown fate isn’t gimmick but an essential contribution to both characters’ arcs. 2) In Book 1 Victim must have her own story of struggle substantial enough to carry the book to its cliffhanger. Victim’s plot and character arcs in Book 1 should then stoke Driver’s arcs in Book 2, with all arcs merging in Book 3. Like those ideas?