Direct answer
Objectives follow journal display order. Some depend on your choices; follow the active objective in the game.
Result
While unheroically roaming the backcountry that was the Champs-Désolés, our heroic witcher was ambushed by a pack of ne'er-do-well highway robbers. He quickly dispatched the upstart traveler molesters, then prompted by curiosity, searched their encampment. He found an interesting letter.
