A LIBRARY-BASED PROPOSAL:
I retrieved my Proust, and opened it up to find that a ring box-sized hole had been carved from it, at which point I checked to ensure that this was not, indeed a library copy. (Aside: thanks to Jimmy at FreeHollowBooks for his fabulous work) Inside the hole was a specially made ring box with the date and my and partner’s initials carved into it. And inside the box was a vintage 1930s-era ring.
Very sweet.