William couldn't watch the door from here, but he could get up and check the study areas every now and then, and the students knew to find him if he wasn't at the front desk. He spent enough time reshelving and researching for them to be used to playing hide-and-seek-the-librarian. It was quiet back here; Spencer might be able to at least close his eyes and rest.
He drew his wand and flicked it in the direction of his desk, a quick accio Summoning the list he'd been working on, with a quill drifting whimsically along in its wake.
"Go to sleep," he told Spencer with a faint smile. "I'll be here."