He simply did not want to leave it in its original place.
The book was returned to its previous spot by Dominic, who turned off the light and climbed into bed. But he could not fall asleep, the restless feeling suddenly made him feel irritable.
The fact that Lucien liked him was, naturally, something Dominic had guessed a long time ago. He did not even need to guess; when was this youth not hanging the phrase "I like you" on his lips? But even so, after reading that letter, his mind was filled with the image of Lucien trotting to the door to welcome him every afternoon, his hands still covered in flour, his smiling eyes curving like crescent moons.
