The reading
The bead. A teenager stranded in his parents' past has to engineer their love story to exist at all — and gets home to a family remade better than the one he left.
Engines
- homecoming/reunion · content · spine · ~ — the engine is literal: Marty is displaced in time and the whole plot is the drive to get back — to his own present, his family, his girlfriend. The payout is the return home, the timeline restored (and improved).
- repricing · content · also-runs · ~ — the McFly family revalued: timid George, bullied by Biff, is engineered into a man who stands up for himself, so Marty returns to a confident, successful family in place of the dejected one — the discounted father (and clan) revalued.
The bundle. A homecoming/reunion spine (get back to 1985) braided with repricing (the family transformed) — the return is to a better version of home than the one departed.
Dual-use read. Homecoming's counterfeit is the nostalgic "restore the golden past" pitch; Back to the Future plays with it benignly — the past is meddled with not to restore a myth but to fix a real harm (George's lifelong cowing), and the improved present is earned by an act of courage, not magic.
Verdict. A homecoming/reunion spine with a repricing payoff — get home, and find the family revalued in the bargain.
Evidence. ~ reviewed — from the film (in-copyright).