Ah. Malcolm had been so caught up in trying to make Will miss the deadline that he hadn't realised just being in the shed at all was probably awful for him.
"On second thought," Malcolm said with a smile, "I think I'll leave you. Give you the weekend to stew." He withdrew slowly, sure Will could hear him leave, as well as his immortal presence move away.
He wasn't actually going to leave Will there all weekend, but he wanted to see how Will was going to react to the possibility of it.