The episode begins and Danny and Lansing are busy arguing about the pronunciation of a word, while at office. In the end Danny is proven right. The Sergeant comes in and informs them that two cars have gone over the “guard rail” at a bridge. “Since when do detectives catch car accidents?” Lansing comments. “When they don’t think they are accidents” Danny replies. They arrive at the scene and are informed that the drivers of both the cars are dead. One of them was a woman who was driving an SUV. Danny looks at the woman’s body and sees a bullet wound in her temple. Incidentally that is the cause of death and not the accident.
Garrett arrives at Frank’s office and tells him how two people on a highway were shot with the same gun, just two weeks apart. Garrett feels “this is a serial sniper” a hit man who is taking out innocent civilians. Garrett wants Frank to hold a press conference about this so that everyone in the city can be alerted. But, it turns out Frank was going to hold a press conference all along. Sean in the meantime has a biking accident while riding with Erin. He is rendered senseless. Erin in panic calls 911. The EMT’s arrives a little later and rush him to the hospital. At the station Danny tells the Sergeant about the two people who were shot by the sniper. The first victim is a man named Gerald and the second is the woman who was recently killed named Angela.
Danny also tells the Sergeant about an empty food packet found from inside a trash can near the spot from where the shooter shot the first victim. The food packet is from an obscure eating joint that serves health food. The Sergeant feels Danny is grasping at straws, but Danny feels otherwise. He convinces the Sergeant by showing him another food packet from the same eating joint found in a trash can near the site of the second shooting. Just then, Danny gets a call about Sean’s accident and so do the other Reagan family members. At the hospital the doctor informs Danny and Linda that Sean has suffered significant brain trauma, which has resulted in his brain swelling up. She adds that she can’t say for sure if there is any brain damage till the swelling comes down. The doctor eventually says that the whole thing will have to be given a few days, so as get a clearer picture.
At work, Frank was told by the Mayor not to go public with news about the sniper, as it would affect the holiday season, but when another man is killed by the sniper, Frank decides to go public despite the Mayor’s orders. Garrett feels it’s a bad idea for Frank to go against the Mayor, but Frank wants to do the right thing. Later, the Mayor reprimands Frank for going ahead with the press conference, but Frank maintains that he did nothing wrong. At the hospital, Erin gives Danny courage and asks him to have faith. Jamie tells Danny about how the bullets used by the shooter are made of bismuth instead of lead. Jamie points out how that is more environmentally friendly than using lead. Jamie gives Danny the details about a company that used to make environmentally friendly ammo and just recently went out of business.
He also tells Danny that, this company used to make bullets of the exact same caliber the killer has used. He then gives Danny the name of a guy -- Peter Westlick, who bought a lot of stuff at a “fire sale” when the company went out of business. Danny reluctantly leaves to deal with the case. Linda encourages him to go, as she feels he would drive himself crazy if he stayed at the hospital. Danny and team later storm Peter’s house. They discover that Peter is an artist and has used the bullets in his painting. Basically he has stuck all the bullets to his painting. Danny is frustrated and tells Lansing they are overlooking something. He comments on how they have stuff connecting the shooter, but they have nothing connecting the victims. But, Danny is sure the shooter’s victims aren’t random and he is choosing them for a reason.
The two in the end conclude the thing connecting the victims are their cars. They tell the Sergeant how all the vehicles the victims were driving were “gas guzzlers”. “Our shooter is trying to save the environment, one dead motorist at a time” Danny says. Lansing suggests they start going through all the “hardcore green groups” in the city. The Sergeant agrees with her suggestion and gives her and Danny the go ahead. At the offices of one of these groups a guy named Leaf tells the two that he had met a military guy at a rally, who had mentioned he wanted to kill people who don’t care about the environment. Leaf thought he was crazy and therefore didn’t entertain him. Leaf has pictures of the rally on his cell phone, from where Lansing hopes they can get this military guy’s face.
They get the guy’s picture from Leaf and head to the health food place, to see if anybody there recognizes the guy. The guy at the counter in the health food place does not recognize the military guy from his picture. The two, then decide to run the picture through the system and see if the guy’s military record shows up. Later at the office, after running the guy’s picture through the system, Lansing manages to dig up the guy’s military record and his other details. Lansing informs Danny that the guy’s name is Matt Hinkle; she also gives Danny his address. The two then arrive outside his apartment along with their team. They knock on Hinkle’s door and ask him to open up, but there is no response. They storm the apartment and see Hinkle dead on the couch. Turns out, he shot himself in the head with a handgun.
In the apartment they also find the rifle Hinkle used to kill his victims. Both Lansing and Danny find it odd that Hinkle shot himself just before they arrived. They both conclude that it was probably Leaf who gave Hinkle the “heads up”. Danny concludes that Hinkle’s death wasn’t a suicide after all. This is confirmed when Lansing informs Danny from Hinkle’s military report that he was left-handed, but Danny sees that Hinkle has been shot on the right side of his head. Lansing and Danny are now sure that Leaf staged the whole thing, including planting the rifle in Hinkle’s apartment. They arrive outside Leaf’s apartment building and see him getting on a bike. They yell out to him. He on seeing them speeds away on his bike. Danny runs after him.
Eventually Leaf crashes his bike into an oncoming vehicle and falls to the ground. Danny handcuffs him and places him under arrest. The next day, the Mayor commends Frank for a job well done and apologizes to him for earlier. He asks Frank to go and be with his family at this trying hour. At the hospital, Sean eventually wakes up from his coma. Frank and Danny are in the room. Frank goes out and calls Linda in. They are all visibly relieved to see Sean awake. Danny later pays his brother, Joe’s grave a visit. The episode ends at this point.