Borrower’s Bookmark

A neat strap of embossed leather, the borrower’s bookmark can be placed in a book, allowing it to be stored in an extradimensional space. As an action you can send the book into a pocket dimension. While it is in the pocket dimension, you can use an action to summon it to your hand or an unoccupied space within 5 feet of you. If you unattune from the bookmark while its book is within the pocket dimension, the bookmark reappears on your person, but the book is lost. The bookmark’s magic can’t be used to store anything other than a book.

Curse. The borrower’s bookmark is cursed. Books dismissed to the pocket dimension are sent to a powerful entity’s lair. The entity learns all the knowledge contained therein, as well as your identity and location.