Train Wreck victims come to Seattle Grace and all staff gets called in. Everyone deals with really weird cases. Except Addison and Izzie. They work with a woman who is pregnant.

Meredith tries to avoid the Shepherds. Cristina and Burke go out on a date and end up getting caught up in their jobs. Derek asks Meredith not to ignore him until Addison comes walking around the corner.

The hospital staff is left to deal with the aftermath of George's passing. Hitting the staff hard, they all find unique ways to get through the various stages of grief. George's mom returns, faced with the difficult task of deciding what to do with his organs.

The residents of Seattle Grace and Mercy West vie for surgeries and their careers as day one of the hospital merger begins. Meanwhile, Arizona stands by an enraged Callie when her father, Mr. Torres, employs a priest to help convince her to date men, and Izzie experiences the brunt of her new surgical competition.

A gunman opens fire at a local college, sending mass casualties to the hospital; Arizona's return is not warmly received.

After a roller coaster car falls off the track at the county fair, the doctors at Grey Sloan tend to patients who spark memories about ghosts from their past. The series 300th episode!