On Grey's Anatomy Season 10 Episode 19, the doctors will focus on a boy without an immune system.

What happens when this young man escapes his protective bubble and runs out into the hallway? Some scary stuff for everyone else in the area, that's what.

Check out this sneak peek now:

Elsewhere during the hour, Cristina will try to temper her excitement over a Harper Avery nomination, while Alex ponders a change Derek/Callie work with a machine that can recognize emotions.

Pretty cool, huh?

Watch Grey's Anatomy online if you need a refresher and return to TV Fanatic Thursday night for a detailed recap/review of "I'm Winning."

Matt Richenthal is the Editor in Chief of TV Fanatic. Follow him on Twitter and on Google+.