While working the busy clinic, Foreman suggests to Thirteen that she participate in a clinical drug trial for Huntington's disease. She turns him down. Meanwhile, House is in Cuddy's office, snooping. A frustrated ER patient named Jason pulls a gun and holds the patients and the staff hostage in Cuddy's office. This includes House and Thirteen. Jason demands that House look at his medical records in order to diagnosis his symptoms, which other doctors have failed to do. He suffers from lack of breath, fatigue, headaches, stomachaches, skin rashes, heart palpitations and insomnia.
As everyone else is evacuating, Cuddy arrives at the hospital. House tries to get inside Jason's head. He hands a lighter to Jason and instructs him to hold it out as far and see if he can blow it out. When Jason blows, the lighter only flickers. House says it can only be pulmonary scleroderma. Cuddy calls, and House asks her for propofol to treat it. Cuddy brings up the meds, and Jason, sensing he's being set up, demands that House give it to someone else first. House picks the biggest guy in the room. As House is about to give Jason the injection, the other man collapses. Jason is angered and shoots a hostage in the leg.
SWAT team members finally arrive on the scene. House speaks to Foreman, Taub, Kutner, Cameron and Chase on the speakerphone. Chase won't get involved and walks out. Foreman suggests that Jason has chronic lung infection. Thirteen thinks it could be a cancer spread from the lungs. Kutner recommends poor circulation or a congenital heart defect. House plans to get a sample of Jason's blood, instructing Foreman to run tests for infection or cancer. He wants Cameron to comb through the man's medical records. Taub and Kutner will to go to his apartment to look for neurotoxins. Yet Jason hangs up the phone when he hears the SWAT team surrounding the window.
Jason points the gun at Thirteen and threatens to kill her unless they back off. House and Thirteen check for nerve palsy on Jason because his hearing was so strong. They notice that one of the man's lip corner is slightly lower than the other. The left-side facial weakness means seventh-nerve palsy. House diagnoses post-herpetic neuralgia. Jason wants proof even though the test is more painful than the treatment. Jason releases the two injured hostages in exchange for the Capsasin.
House gets the vials of blood and file to Cuddy. Thirteen volunteers to be the one to take the first dose. House injects her and then injects Jason. They both recoil in pain. House walks toward the wall that he is using for a whiteboard diagnostic and crosses off "peripheral nerve paralysis."
Taub and Kutner check out Jason's clean and barren apartment while Foreman and Cameron run blood tests. House crosses chronic lung infection off the wall leaving congenital heart defect and lung cancer as the possible causes.
The hostages, particularly Thirteen, are weary. Kutner reports back that he found a picture of Jason's mother, whose face shows signs of an upper-lobe tumor or an adrenal problem. Thirteen says it's the heart. She points out to House that Jason's neck has a distended jugular. House presses his finger deep into one side of Jason's neck to check pulse, performing a Carotid massage to try to slow the heart. The terrified hostages watch as Jason now aims directly at House.
Thirteen suggests that they cardiovert chemically. She is permitted 30 seconds to retrieve the Adenosine from a cart. The SWAT team urges her to escape, but she returns just in time to save hostages from being shot. Thirteen quickly injects herself. Within seconds, she gets weak and collapses to the floor.
House takes the other syringe and jams it into Jason's arm. He calms down. There is no sign of a heart defect at all, but Jason is sweating only on one side of his face. This is called anhidrosis. A tumor is pressing on his sympathetic nerves, which indicates lung cancer. With Thirteen barely conscious, Jason insists on proof. House calls Wilson, and they agree it is a metastasized Pancoast tumor.
Two more hostages are released. The remaining hostages have been arranged in a protective circle around Jason as they cautiously proceed through the clinic doors to the elevator. They walk slowly toward radiology. The empty hall suddenly begin filling with SWAT officers. House and Thirteen administer the CAT scan to Jason as he listens from inside the cylinder with the gun still pointed out the opening. Jason admits he can't handle not knowing and needs answers. House tells him that the gun has interfered with the imaging. He has two choices: turn over the gun and get an answer or he can shoot House.
Two more hostages run out. Gun in hand, House examines the images as Jason lies in the machine. There is no tumor. House is unable to diagnose. Thirteen and House spar under the pressure. House hands Jason back the gun.
Wilson, Foreman, Kutner, Taub and Cameron are nervously gathered. House calls them with the symptoms: dyspnea, anemia, seventh-nerve palsy and tachycardia. Foreman walks out. The team seeks suggestions when House notices that Jason's head tilts to one side. Cameron suggests Cushing's disease. It causes fatigue, breathing problems, fluctuating hearing, as well as increased aggression and risk-taking.
The last hostage escapes, and House takes a vial of dexamethosone from Cuddy. Although he agreed not to use Thirteen, Jason insists that she be the one to sample the medicine for him. Thirteen takes the syringe from House and injects herself in her leg. House injects Jason in the leg. Thirteen passes out. Her kidneys are shutting down. Jason is unaffected. His kidneys should be failing but something is protecting them. House slaps Jason across the top of his jaw. Jason's facial muscles on that side twitch rapidly. House slaps him on the other side and gets the same twitch. That twitch is Chvostek's sign. His medications have been protecting his kidneys for years.
Jason has something with a long incubation period. Cameron comes up with Melioidosis. Jason says he has not been to a tropical climate but has been to Florida, which he did not state on his patient history. House calls for more meds, and Jason offers to trade them for House's freedom. House argues to keep him and release Thirteen. She tells House to leave. Either the drugs will kill her or this man will. A SWAT officer throws a small bag of meds into the room then moves in to attach an explosive frame charge to the wall.
Thirteen tells Jason that she does not want to die, but Jason thinks she does -- she just doesn't have the nerve. Thirteen holds the syringe to herself and Jason finally gives in. He quickly drops the gun and grabs the syringe from her to stab it into his own arm. The wall explodes open. As Jason and Thirteen are brushed back, officers storm in. House enters to tend to Thirteen.
House pops some pills in the lobby and looks as SWAT officers lead Jason away in cuffs. Thirteen lies in a hospital bed on dialysis. She tells Foreman that he was right to suggest a drug trial for Huntington's.
As Cuddy surveys the damage to her office, House enters to fetch his cane. He tells her that tests confirmed melioidosis. They disagree about their relationship, or lack thereof. House takes his cane and exits. Cuddy sits behind her desk and pulls open a drawer. Everything falls to the floor. House was in her office that morning to turn her drawer upside-down. House hears the crash, but is now only able to find slight pleasure in the prank.