Credit: Ron Tom/ ABC

Grey’s Anatomy is about to go into hibernation for a final Season 9 hiatus, but before it leaves us hanging for a few weeks, a big episode is happening tonight, April 4, 2013.

Season 9, Episode 20: “She’s Killing Me” is jam-packed with a few notable storylines, including the big reveal of Meredith’s Alzheimer’s genetic markers, a scary and mysterious infectious outbreak at the hospital, April and Matthew drama, and a few new doctors.

From the sounds of it, this dramatic episode will be quite a doozy. We’ve speculated that the “investigator” will come by in this episode, though the main focus of the drama could be around Meredith and Derek — she does insist that they “call the lawyer,” after all.

Either way, there’s a lot to prepare for until the episode airs tonight, so make sure to watch the promo on repeat, check out all of our latest sneak peeks, and cross your fingers that all of our Sloan Grey Memorial Hospital docs make it out of the “outbreak” alive!

Grey’s Anatomy airs tonight, Thursday, April 4, 2013 at 9 p.m. ET on ABC.