Shaun and Lea dance happily at their wedding while Andrews and Glassman walk off and Park looks sad.

Lim is bleeding but not dead. She checks on Dulce then tries to call Andrews for help but he can't understand what she is saying as he is in the elevator.

The bad guy is int he elevator too and Andrews notices he is bleeding. The guy claims to be a psychiatrist who was attacked by a patient. They all get out and the security guards try to arrest him but he grabs a gun (seriously) and begins shooting randomly while two other cops shoot at him. He runs away shooting and Andrews tells Glassman Code Silver, Lockdown (while no one else can hear because no one else is there.)

The hospital has been locked down and Andrews and Glassman realize the shooter came from the fifth floor where Lim was headed. They need trauma bags and rush to help her.

Somehow Shaun finds out about this and decides he's going in to help. Lea doesn't want him to but he won't listen. Jordan goes too. Lea refuses to wait alone.

Asher and Morgan find a patient on a bench in the hospital (is he seriously the only one there during this lockdown?" and sneak him into an exam room. He has Chron's disease and may need surgery.

Shaun and Jordan find the  bloody crime scene. Shaun takes off his belt to use to help stop the bleeding. Yep, we've gone full MacGyver here. Glassman and Andrews arrive. Lim's heartbeat is weak and she may be dying.

The women are taken to a trauma unit. There's no blood available for transfusion. Shaun asks Lea to act as a nurse and get supplies as needed. Lea cries as she scrubs in.

Glassman and Shaun disagree about how to handle Lim's procedure. Glassman wants a more conservative procedure that may shorten Lim's life expectancy. He leaves to tend to Villaneuva and, to no one's surprise, Shaun decides to do things his way. Glassman and Andrews also disagree about how to treat Villanueva's injuries.

Also unsurprising: Asher leaves to get supplies for their patient and gets held at gunpoint as he returns.

Morgan tells the patient to be quiet. She hears a scuffle in the hall as Asher tries to explain he needs to get supplies to this patient. She opens the door. No Asher, just a tray of supplies.

Meanwhile, Glassman returns and is angry that Shaun changed the plan without permission. It's too late to change now. He joins the surgery. Lim starts bleeding. Glassman wants to undo the packing and do it his way (don't they have to stop the bleed first regardless?) Shaun says injecting particles will stop the bleeding. BP rises. Shaun was right.

The gunman wants Asher to get him out of the building, which is impossible. He exchanges fire with a cop and decides to go into the room with the patient. He says he will kill Asher if Morgan doesn't let him in. Asher says don't but Morgan doesn't listen. The gunman forces his way in and locks himself in with them. He wants to know how Villanueva is and claims he loves her.

Andrews gets word of the hostage situation somehow and tells Jerome.

The gunman allows Morgan to call Park who says they can't do the surgery there safely. She tells Park she loves him and hangs up. She claims that she spoke to the OR and that everyone the gunman hurt will be okay. But if he lets this man die he will be charged with murder. The gunman tells Asher to come with him.

Lim wakes up but can't speak. They fill her in. She starts crashing. It's her heart.

Asher convinces the gunman to surrender. The guy unloads the gun and goes out but instead of surrendering attempts to shoot with his empty gun and is shot.

There is only enough bypass for one patient. Lim needs it and so does the gunman. Shaun says Lim needs it more. He is overruled by Glassman and looks like he is about to melt down.

Sure enough, during the surgery Lim's heart starts to fail. Shaun has some flashbacks of his brother's death and freaks out. He has to be dragged out of the room by Jerome.

Glassman and Lea try to talk to a catatonic Shaun in the hall. Shaun sees a vision of a grown-up Steve telling him it's not his fault that Steve died. Glassman has to get into the OR. They video call Shaun. He realizes what the problem is.

Shaun successfully completes Lim's surgery. Soon, the lockdown is lifted. The gunman wakes up cuffed to a bed and everyone else survives.

Park and Morgan talk. Morgan has decided not to take the job. Park thinks she should take it. She always will put her career over him. She says she changed today. Park thinks it's only temporary.

While checking on Lim, Shaun realizes she is paralyzed.