In the present, Allie becomes briefly lucid and remembers that the story Duke is reading is the story of how they met, as Duke tells her of a younger Allie appearing at Noah's doorstep, having left Lon at the hotel.
Allie becomes briefly lucid. This is in the present. The story is the story of how they met, as Duke tells her of a younger Allie, having left Lon at the hotel. This is what Allie remembers in the present. This younger Allie is appearing at Noah's doorstep. Duke is reading The story.