V nemocnici námořnictva dojde ke vznícení pacienta po operaci srdeční chlopně. NCIS je k případu přivolána, aby vyšetřila, zda se jednalo o nešťastnou náhodu nebo o mnohem závažnější situaci. Díky pitvě se zjistí, že šlo o vraždu. Z této vraždy je podezřelý námořník, který měl s obětí, jež byla jeho velitelem, spory. Tento námořník se také ze svého pracoviště ztratí a když ho lidé z NCIS najdou, pokouší se před nimi spáchat sebevraždu. Caitlin ho v domění, že při manipulaci se zbraní v ruce chce ohrozit Gibbse, zastřelí. Další vyšetřování však odhalí, že pacient byl už v době vznícení mrtvý a námořník nebyl jeho vrahem.

Open at a hospital where the orderly has just checked in on a patient. In the hallway his doctor inquires if he is asleep and the orderly says that Dr. Byers made sure of it, gave him Percocet. Then just as the doctor replies that if the patient had called her in at 2 AM she would have killed him, the patient's room explodes.
Opening Credits

Gibbs is in his basement working on the boat, hand drilling holes for dowels, with the crop report on in the background. Tony calls, hoping he didn’t wake Gibbs. Cut to a shot of the mystery redhead looking over the boat plans. Gibbs asks if she can drop him at Bethesda.
At Bethesda Navel Hospital Tony notes how quickly Kate got there. He implies she was not in her own bed and wants to know where she was. She tells him to drop it as the mystery redhead pulls up with Gibbs. Tony thinks he and McGee were the only ones alone last night, McGee tells him to speak for himself, which is a real blow to Tony. Tony fills Gibbs in on the details. An explosion, causes unknown, resulted in Michael Dornan, a safety officer on the Kennedy, to go up in flames. He had open heart surgery four days ago.
In the patient's room Ducky and Palmer have begun their examination. Ducky says the source of the fire seems to be internal with most of the damage confined to the torso. Kate notes that he was on an oxygen tube, but Ducky isn’t sure that would result in this much damage and still needs a source of ignition. Kate finds matches and cigarettes but he was asleep, so that's not it. McGee thinks it's spontaneous human combustion and gets a “look” from Gibbs. Although, Ducky says not to rule it out.
Gibbs is interviewing the patient’s doctor. She says he insisted she be called when he experienced some post-op pain last night. She did an echo-cardiac exam and he was fine and she gave him the Percocet for the pain. On his way out Ducky runs into them, it is apparent he is somewhat smitten. He ends up getting her numbers.
Down in the garage Abby is examining the hospital bed and imploring Gibbs to give the SHC (spontaneous human combustion) theory a chance. Even gives him precedent. Apparently her masters degree thesis discussed it. She has determined all the hospital equipment was in perfect working order and not the source of the ignition. She doesn’t have a cause.
In the squadroom Gibbs gets a status report. McGee has found that the oxygen supply was normal and Tony has confirmed that everyone thought he was an ass. As Kate gives her report--divorced, no kids, wife in Santa Fe, her cell phone starts to ring. Tony heads over to check out who is calling, Harrison. Kate inflicts some pain and gets her phone back.
In the lab Abby and Ducky are melding minds in an attempt to figure out the case. They have recreated the explosion and determined the point of ignition. Someone struck a match and ignited the oxygen. But according to the orderly the patient was asleep and it wasn’t an accident, so murder.

Gibbs is handing out orders. McGee is to review the security tapes and figure out how someone got in and out. While Kate and Tony head to Norfolk and the USS Kennedy where Dornan was stationed. Tony is delighted since Paula Cassidy has been reassigned there as Agent Afloat.
On the USS Kennedy Kate takes the opportunity to tease Tony about his relationship with Cassidy. He sends her off to interview the XO. Cassidy doesn’t seem thrilled to see him, complete with banter. Back on the case Cassidy reconfirms that he was not well liked and made enemies as safety officer.
Gibbs and Ducky are discussing how pure oxygen accumulated in the victim’s chest cavity and not the lungs. Ducky doesn’t know. Dr. Byers arrives with copies of Dornan’s medical files for Ducky. They have a “moment” before he asks her why she chose to do a valve repair instead of a valve replacement. Cmdr. Dornann was insistent; if they replaced the valve he would not be allowed to go back on active duty.
Agent Cassidy has returned to DC with Kate and Tony to help with the case. She identifies an individual McGee found during his search of the surveillance tapes, as Ensign Evan Hayes. Cmdr. Dornan came down hard on him, more so than any other. It got to the point Hayes verbally threatened him. Gibbs asks Tony for the incident report but Cassidy says there isn’t one. Dornan had asked her not to file one, that he would handle it himself. Gibbs chews her out.
Back on the Kennedy Tony and Cassidy are informed that Hayes was restricted to ship by Dornan. However, he went UA (unauthorized leave), walked off 2 days ago. The Chief tells them that both he and Dornan served under Hayes’ father, who came down hard on Dornan. He in turn used this cruise as pay back.
Abby was able to salvage the last 7 minutes of vitals off the hospital machine. She passes the info on to Ducky noting his spiffy bowtie. He confesses a date with Dr Byers. He plans to take her somewhere that expresses who he is; if she enjoys it too then they aren’t wasting their time.
Hayes has dropped by what looks like his old high school to talk to his former swim coach. His coach is surprised to see him, Hayes had promised he would go back to the ship. Coach is worried he is throwing away his career. As Hayes is leaving he discreetly checks the clip in his gun.

Back at the bullpen McGee and Kate are doing background on Hayes and trying to figure out the timeline. On the Kennedy Tony is actively pursuing Cassidy who is still shooting him down. While in the lab Abby is reviewing the evidence, she decides something is missing. Palmer is testing out talking to the deceased when Abby sneaks up and scares him. She wants Ducky, but he has left early without his cell phone.
Ducky has taken his date, Dr. Byers, to the basement of the Smithsonian. It where they prepare the exhibits. Specifically the display has the tools used for President Lincoln's postmortem. He has set up a romantic dinner for them down there. He inquires how she ended up in the Navy and she tells him she is actually leaving to accept an offer in New York.
In the squadroom McGee is madly working and Kate wants to know why Gibbs is being so hard on Cassidy. “You made her spend the day alone with DiNozzo.” “She survived.” McGee just finds out that Hayes' credit card has been used to pay for a hotel room. The team moves out; Tony and Cassidy will meet them there.
The hotel clerk is giving Gibbs and Kate a hard time. He won't tell them what room Hayes is in without a warrant, apparently he is a law student. They get the key, loud music is coming from the room and upon entering they find three couples making out. None of them are Hayes. One of them confesses that some guy gave it to him after swim practice, said he didn’t need it anymore. He wanted to use the pool at the high school. Cassidy and Tony are left to babysit them until the parents arrive.
At the high school Kate and Gibbs find a depressed Hayes at the pool. He puts the gun to his head as Kate and Gibbs approach. Hayes tells Gibbs to put down his weapon, he does so and Hayes lowers his. Hayes says he’s a coward, been trying to pull the trigger all night and can’t. Hayes stands and raises his gun and Kate fires.

In autopsy the swim coach identifies Hayes’ body and gives him an alibi for the time Dornan was killed. Kate is very upset, says he must have the time wrong. She is terrified the man she shot was not a killer. Gibbs sends her out of the room. Gibbs continues the interview. Hayes had told the coach he had gone to the hospital to confront someone, but lost his nerve. It was suicide by cop.
In the squadroom McGee is still reviewing the tapes trying to identify everyone. Cassidy tries to explain her actions, but Gibbs won't hear it, and sends her back to the ship. Tony is to go back to the lab to review all the physical evidence again.
A very chipper Ducky arrives in the lab. Palmer gives him the info Abby brought down the night before. He immediately wants Cmdr. Dornan’s remains back on the table and calls Kate. He wants a service record.
Tony is screwing around in the lab and basically bugging Abby. He begins to “examine” the evidence, but gets serious when he picks up the bag with the matches and cigarettes. Tony has figured out how the oxygen was ignited. While they wait for Gibbs they play “mirror image” through the glass. Tony, who is facing the door, ducks when he sees Gibbs coming. Tony’s theory-- it was used in a movie--is that a lit cigarette was used as a time fuse. It would take 12 minutes for it ignite the match book and oxygen line. Who was there 12 minutes before the explosion? Dr. Byers. As they are leaving the lab Ducky arrives to inform them he wasn’t murdered, he died as a result of his surgery. Dr Byers made it look as if he was murdered. She was trying to cover up her mistake. She was brought up for malpractice in 1995 for a heart valve repair almost identical to the one she performed on Cmdr. Dornan. Ducky compared the last EKG recorded to previous ones, the last was not his.
Ducky accompanies Gibbs to the hospital to confront Dr. Byers. He tells her there was no Percocet in the Cmdr’s stomach. She replies she is glad it's over, she says when she arrived at the hospital it was apparent his valve was failing. It needed to be replaced but when she told him he became hysterical and went into cardiac arrest. A second valve repair failure would end her career and her new job. She explains how she did it, Ducky tries to tell her she didn’t kill him.
In the squadroom Tony is only getting Cassidy’s voice mail and McGee is off on a date. Ducky is concerned that he has two tickets for the opera and now no one to accompany him. Gibbs says no. Ducky wonders if Kate would like to go. But she is downstairs in autopsy, staring at Hayes’ body.