Returning "Persuasion" to Kate
Other than it being a quirky, "ta-dah" moment in the film, why did Alex go to what must have been considerable trouble hiding the book under the floorboards of a building mid-construction, making Kate wait several extra months for a treasured book she'd expressly asked him to retrieve [and then not telling her!!...] when he could have sent it to her via the mail box, as had happened with the scarf?
I mean, we all like a romantic gesture- but surely just returning the book was romance enough, without showing off?