The season 12 premiere of "Grey's Anatomy" saw a return to the show's lighter, more humorous side after the shocking events of season 11. After the one-year time jump, Meredith (Ellen Pompeo) has already gone through the worst part of grieving Derek and has gone back to work. Meanwhile, Bailey (Chandra Wilson) became the hospital's first ever female chief of surgery after competing for the position with another woman.

In "Walking Tall," the second episode of season 12, the hour will focus on April (Sarah Drew). Having just come back from the Middle East, it seems like she brought something else home aside from her memories of her travels..

In the teaser trailer, April is back and she's asking Arizona (Jessica Capshaw) if she missed Bailey's party. She tells Arizona that she couldn't stop sleeping and thinks she's simply fighting off a cold or jet lag. Upon removing her shirt, it can be seen that she has a lot of rashes on her back.

"What the hell is that?" Arizona exclaims. "On your back!"

"What, what's on my back? Do I have a mole or something?" asks April, who's twisting around as she tries to see what's on her back.

Arizona grabs a facemask as April starts coughing, and the scene cuts to the hospital, where April is now inside an isolation chamber. She tries to reason with Arizona, Bailey, and Jackson (Jesse Williams), saying that all she has is "a stupid rash" and that everyone is overreacting.

"I'm sorry, I work with babies," Arizona says in hopes that April will forgive her for bringing her there.

"Kepner, you've got lesions, a cough, a fever. You were in the Middle East!" Bailey points out. April says that she has been traveling and is run down, but Bailey says they don't know what she has and furthermore, they don't know how contagious she is, thus the need to keep her isolated.

"Hey, this is my first day running this place, there will be no epidemics today!" says Bailey. She turns to April and says that until her tests come back, she stays in isolation.

"This stops with Patient Zero!" Bailey says.

"Grey's Anatomy" airs on Thursdays at 8 p.m. on ABC.