Upon further reflection, I think if you're doing a flashback, there may
not even be reason to avoid framing the final contest to be about
catching the kidnappers. If it turns out they *didn't* catch the
kidnappers, what does that mean? Does it mean they've been lying about
it all this time? Does it mean they only thought they captured the
kidnappers but the audience now knows that wasn't true? Does it mean
someone died in the rescue that they haven't mentioned? In other words,
anything that comes up in the flashback can be meat to the story that
they haven't told yet. Now, if everyone knows they caught them, and
there is no interest in that turning out to be only a piece of the
truth, then you should avoid this. Otherwise, why railroad them? See
what happens when they play it out, and note details that can come back
later. Flashbacks are a great storytelling device for showing us
something new about the characters.
Just my 2 cents,
LC