Severus Snape was a meticulous man. He had deeply ingrained habits and routines, habits and routines out of which, in the three years that they had been shagging, Harry had never been able to budge him. The Potions master also had rituals, and one of these, Harry had been amused to discover, was the doing of his own wash.
Severus' clothing was black unless it was white—black robes, jackets, vests, trousers and socks; white y-fronts, undershirts, and dress shirts. Each month, he would replenish his supply of personal washing potions and then disappear into a small room in his quarters which boasted good ventilation, a massive cauldron, and nothing else. It was his laundry room, and he never permitted Harry to enter it.
But Harry had entered it because Severus had been asked, last-minute, to make the opening remarks at the International Guild of Potions Masters' annual lecture series. In his haste to leave, he had forgotten, apparently, that he would be gone until the second of May, and Harry had thought it would be a nice gesture for him to do Severus' laundry—thus preserving his lover's routine, if not his ritual.
That had been his first mistake.
His second had been using conjured Muggle detergent.
His third, or perhaps actually his first, Harry could not decide, was forgetting why it was so very important to Severus that his whites be spectacularly so.
And now I'm pulling grayish-blue pants out of "the Cauldron," Harry thought, panicking. "Severus is going to kill me."
"Why," said a dangerously low voice from the threshold of the laundry room, "would I do that?"
"Severus!" Harry exclaimed, dumping the ruined clothing back into the cauldron in hopes that it had not been seen. "What are you doing—"
"A better question, I think, would be what are you doing?"
"All right—your wash," Harry said guiltily, holding up a pair of less-than-spectacularly-white pants. "I'm sorry. I was just trying to be helpful. I know how much you hate—"
Severus began to laugh.
Laughter was not one of his habits, and Harry was gobsmacked into silence.
"You . . . you foolish—did you really think I was going to hex you for . . . for ruining my laundry?"
"No, I thought you were going to kill me."
"Someone should know about this," Severus replied, composing himself and leaning against the doorjamb.
"Your terror of disappointing me. Your appalling lack of Potions knowledge. Your delectable lower lip—no, not that," Severus corrected himself, as he walked toward Harry. "That delectable lower lip is mine."
Suddenly Harry found himself pressed between a warm cauldron and a hot Potions master, but he found he did not mind as Severus began kissing him breathless.
Sometime later, Harry asked, "Why'd you come home early?"
Because it was laundry day, Severus thought, mentally making a note to order new clothing as he said, "Because I missed you."
In his three years of shagging Hogwarts' Defense professor, he had learned that what Harry needed most was to be reassured—and to be shagged as often as possible.
It was part of his routine.