[Off teaching entitled brats a lesson, that's where Sebastian is. And possibly killing off a quarter of all the monsters all by himself. For science, you see; just to make out what they're really made of.
Sebastian had plans for his return to Ciel and Madam Red. He'd stop by the apartment to change outfits, because it's terribly unbecoming for a servant to show himself in bloodied clothes, and he'd bring Madam Red a monster specimen to have a look at, if she'd like. She knows her anatomy - perhaps by examining a dead wasp she'd be able to tell something about how they work or where they come from, or some such. He'd find a box or a bag to put it in, of course; it'd be even more unbecoming to present her with a bloody carcass just like that.
But Sebastian rethinks this. If there's one disagreeable little creep with too much curiosity regarding his master, who's to say there aren't more? Why, Sebastian can think of two more demon scum around these parts just off the top of his head, and that's saying nothing of the good Madam. Before, he'd figured he'd made it clear enough (in that unspoken way a clever woman such as Madam Red should understand quite easily) that, should she so much as think about laying a finger on her nephew, Sebastian would deal with that accordingly.
Now he rethinks this. Very convenient, isn't it, to have Sebastian off to scout while she is left alone with Ciel (nevermind that this was Ciel's suggestion, not hers).
Thus, when Sebastian does appear, it's with his suit torn in places and blood running down the fabric, dried blood down the entirity of his neck, blood on his gloves, the corpse of an unfortunate wasp in one hand... Moreover, that's a very cute defense the clinic has set up, with all the doors and windows barricaded. It's only polite to enter through the door, so that's what Sebastian does: he turns the door handle with such force that the lock breaks before simply pushing it open and entering the clinic, completely in spite of anything that had been placed before the door to make it harder to push open.
Now then, he knows exactly where in the building the young master is. Ciel will very soon see Sebastian heading his way, completely disregarding any other person on the way.]