Derek tenses at the sight of the bloody footprints trailing through the loft. "Stiles—"

"Not my blood!" Stiles shouts from the bathroom. "I swear it's not my blood!"

Derek breathes a sigh of relief that he's grateful no one else is around to hear. "I just meant that this is going to be hell to clean up."

"Oh, fuck you," Stiles snaps back, irritated and familiar, and it loosens another knot in Derek's chest.