The episode begins with Mac taking his medicines. He then arrives at the ice-hockey game, where his team is playing against FDNY. Adam is about to give up but Don says that they have two minutes left and that they have a chance to win. But they lose. We see that Mac is friendly with Cutis from the FDNY. But the rest of the teams hate each other and they begin to fight after the game is over. Just then Curtis gets a call about a building on fire in the nearby area. The teams arrive at the scene and the fire department takes charge and goes into the building. Curtis enters a room and just then his suit catches fire and there is an explosion. Next we see the entire team attending the funeral of Capt. Curtis Smith.
Catherine is also present. She holds Mac’s hand. Cut to the scene six months ago; Mac is in the hospital and is recovering. He tells Christine that he cannot remember a thing about him being shot. Catherine helps him remember. Cut to the present, Don tells Mac tha they have their guy in the building at the moment and they have secured the perimeter. Mac and Don go to get the guy. In the building, we see a man standing in one of the rooms. He is taken into custody. Don tells Jo that this man has been their suspect for the fire. He has also been connected to ten earlier fires but they could only the last one on him. He gets out after fifteen years to torture the same building. His name is Leonard Brooks.
Jo wants to know how they grabbed him for the earlier fire as he went inside the building to give CPR to one of the victims. Mac then talks too this man and he tells Mac that he is sorry that he went inside the building during the funeral; bad timing! Mac says that it has only been two weeks since he was released on parole and he burnt down the building. But Leonard denies setting fire on this one as he says that he isn’t stupid enough to hit on the same building twice. Mac then shows him pictures of the previous fires and he tells Mac there is no proof that could tie him to those crimes. Mac tells him that he used wax papers to spread the fire through the hallways. The same residue has been found on this scene.
Mac is losing his calm. Leonard tells him that fire is an addiction for him and many doctors have tried to change him with pills. For the last 15 years, he has been working on his condition and kept himself away from this addiction. He knows that the team waited for him to go to the building after the fire; which he did. But why? Because he too wants to find out who set that fire as he is sure that someone wants to frame him and wants him to stay locked up in prison. He says that as an arson investigator, he needs to go back to study the scene. Next, Don, Mac, and Leonard go to the building. Leonard finds the ignition point. He then asks the detectives if they found anything around this place. Mac says that they found a piece of metal.
Don doesn’t respect Leonard and so Leonard decided not to tell him anything. He says that the ingredients used to torch the building need not link him to this case. The metal was used to give the arsonist enough time to get out before the building ignited. Next, in the office, Mac remembers telling the doctor that he is having trouble recalling and remembering things. The doctor says he is suffering from anomic aphasia. In the lab, Monroe tells Mac that triethyl-aluminum was used to set the fire. Moreover, when this is exposed to water, it gets even more flammable. Monroe also points out to the other things found and they figure out that it there was a trap set up for a fire fighter. Jo and Adam go through the pictures of the onlookers, hoping to find their arsonist.
Jo spots a fire fighter with a code on his hat and she infers by the code that no way he could have gotten there for help. They check his record and they find that the fire fighter is Marshall Hilson and he has been charged with criminal impersonation. He is not even a fireman. Next, Mac interrogates Hilson and he says that he can’t do more than five years. Mac sees that Hilson had applied for a job in the fire department but was rejected several times on basis of psychological issues. Don arrives and says that people have seen Leonard go inside the building and leave before the fire. Mac tells Don that Hilson seems like a buff and wouldn’t be able to pull off such a thing.
Next, there is another fire and one of the FDNY’s team members is beating up Leonard. Don and Mac arrive and Don tackles this fire fighter. He is pissed with Leonard as he murdered his captain. He also found a note in his pocket with the address of the building. Mac arrests Tony, the fire fighter, for assault. Mac then notices that the sprinkler system was turned off and later turned on before the fire started and the FDNY arrived at the scene. So, did Leonard develop a conscience? Mac feels that maybe he had one all along. Hawkes and Monroe run all the prints they found on the scene. But the one on the sprinkler valve outside the building came up with no match. There is fire gel used and Monroe finds a partial logo of something; probably if she could figure out the logo, it could get them to their killer.
Also, there is a sewing needle found at the ignition point. Mac and Don go to talk to Leonard. But Mac is somewhat convinced that Leonard alone isn’t responsible for theses fires. He thinks that maybe there is more than one person involved. Hawkes tells Mac that the prints found on the glove belongs to a woman named Eva Mason, who has been arrested for arson. Eva seems to have visited Leonard several times in prison. She was a a psychology major and she interviewed Leonard three times. She was doing a research on arsonists and pyromaniacs. Hawkes tells them that Monroe ided the logo on the sewing kit, it belongs to River’s Peek motel. As they speak, Jo, Monroe and Danny go to the motel and barge into Eva’s room.
They find a lot of paper clippings and other materials with which she developed her arson devices. Jo starts a laptop and finds a live feed; Eva was watching Leonard. But then they are shocked to see that Eva is at Leonard’s house and she draws a gun at him. Jo calls Mac and tells him to get to Leonard’s apartment as fast as he can. Eva wants to know why Leonard turned the sprinklers back on. He tells her that he wanted to save her from the life he had. She is angry that Leonard is working with the cops. She says that she did all this so that Leonard would be proud of her. He then notices that she has turned the gas burners on and had prepared to blow up his place. She has removed the bulb from the fan.
She says that he should die and the last he sees will be what he loves the most. She turns on the fan switch. The tungsten begins to glow and she tries to open the door to escape. But Leonard pulls the carpet she is standing on and he jumps out of the window. She is terrified and she fidgets with the door locks. But it is late. As Mac and Don arrive, the apartment blows off. Eva’s charred body is lying on the ground. Leonard survives the jump but is badly hurt. At the station, Leonard admits that he did boast a bit, when Eva came to meet him.
He thanks Mac for treating him like a human being and tells him that he doesn’t intend to give in to his addiction as he doesn’t want to go back to prison. Next, Mac gives Christine two dozen roses; one for every week she took care of him. At home, Leonard puts a pot on the burner and he watches the flickering flame. The episode ends.