The episode starts with Meredith and Derek trying to make a baby. Owen’s in bed with Cristina, who seems much better. Lexie and Mark are also in bed together. Arizona’s waiting outside Callie’s door.
Teddy and Henry go to city hall to get married and ask Owen to be the (reluctant) witness.
Meanwhile, Cristina follows ambulances to Pacific College, where a gunman has shot several people. Arizona asks the Chief if she can come back to the hospital, and he explains that he has already replaced her with Dr. Stark. The entire hospital watches the college massacre on TV and gets prepared mentally and logistically to deal with the trauma patients.
Cristina, who’s on the scene, starts giving advice to the paramedics and ends up doing a procedure in the field before surprisingly appearing in one of the ambulances that arrives at Seattle Grace. She seems ok to operate, so she goes straight to the OR.
Dr. Stark wants to amputate a 15-year-old victim’s leg, but Alex argues with him while Arizona watches from above. Arizona and Dr. Stark get into an argument about the patient’s best interest, and then Arizona gets the Chief to reinstate her hospital privileges.
Alex physically blocks Dr. Stark from getting to the patient while Arizona has Callie come and give a second opinion. It is decided that the leg can be saved, so Callie and Arizona end up operating together, much to the dismay of Dr. Stark. Arizona tries to talk to Callie about their personal issues, but Callie just wants to operate.
Meredith and Derek work on another of the patients, a professor who has a brain injury. Meredith is extremely concerned about the patient’s wife and repeatedly leaves the OR to give her updates, which annoys Derek. Meredith and Derek finally have an argument, and Meredith admits that she knows what it’s like to be the terrified wife in the waiting room.
Another patient, Chuck, has a neck wound. Bailey becomes emotionally attached to him and then has Alex finish the procedure. When Chuck almost dies, Bailey loses her cool, but ultimately saves him.
When a police officer requests that the Chief wake up one of the wounded policeman to ask him for a description of the shooter, the chief agrees even though it will cause the policeman a lot of pain. Based on the description, the Chief determines that Teddy and Cristina are actually operating on the shooter.
Jackson storms out of the OR because he is unwilling to help save the shooter when so many victims need medical assistance. Teddy and Cristina stay and continue operating.
Jackson eventually feels sorry for the shooter’s mom, who had no idea that her son was capable of such violence and gives her an update on her son’s medical condition.
Callie cannot forgive Arizona. Derek tells Meredith that Cristina’s back in the OR and that the fishing trip worked. Every victim ultimately survives.
At the end of the episode, everyone goes to watch the surgery on the shooter. Teddy and Cristina save him. All of the doctors break down and cry and then laugh.
The episode ends with the Chief telling Arizona she can come back if she will work under Dr. Stark, Lexie telling Mark she loves him, Teddy having a drink with Henry, and Meredith and Cristina rekindling their friendship in the hallway of the hospital.