"Unless it's some kind of magic virus? What do you think, Will? This isn't like the werewolves back home. I'm thinking if we catch Patient Zero maybe you can magic up a cure? Or maybe someone at the hospital? The City is bound to have a brain or two."
Buffy did a double take and realized that seeing John mostly naked probably wasn't a real introduction.
"God, I'm totally in slayer-mode. Will, this is John Watson. John, this is my best friend, Willow Rosenberg. Find out what you can during the day but both of you should come back before nightfall. At least until we know how this works. I'll try and get cages set up and then patrol."