Alfredo, a construction worker at Cuddy's house, complains that his asthma is acting up. She asks him to finish the job. Alfredo falls off the roof onto the concrete.
An ambulance races Cuddy and Alfredo to the hospital. He can't breathe, and Cuddy notices two of the fingers on his right hand have turned purple. At the hospital, the doctors try to figure out the cause of this. House suggests disseminated intravascular coagulopathy. House asks his team for a cervical MRI and treatment for DIC.
Stacy tells Cuddy that, for legal reasons, she should stay away from Alfredo. Stacy is sure that Cuddy will feel guilty, apologize and offer to pay his bills. The hospital doesn't need that. Cuddy is concerned that Alfredo could lose his hand and then his livelihood.
Alfredo demands to be released so he can go back to work. Chase notices that a third finger is turning purple. Cameron finds that Alfredo isn't clotting properly, which would mean minor DIC. House points out that if the hand is dying, it could move up the arm and further. Cuddy orders a stronger medicine -- human activated protein C. The staff is shocked. House points out that this treatment is only for severe sepsis. It is incredibly dangerous and could cause internal bleeding, strokes and more. Cuddy tells them to do it anyway.
Wilson notes to House that he would've ordered protein C as well. Suddenly, Alfredo screams for help because he can't move his arm. Chase tells Cuddy that the protein C caused bleeding in Alfredo's brain. The treatment is stopped and Alfredo is rushed into neurosurgery. Cuddy observes the surgery.
The surgery fixes the bleed. As Cameron examines him, Alfredo suffers from a coughing fit. A chest x-ray shows lung infiltration. His fingers become darker and he has a fever. Cuddy tries to connect this to Alfredo's falling off her roof. Foreman suggests pneumonia, and Cuddy admits that it is a possibility because Alfredo asked to leave the job. House asks Cuddy to check Alfredo's house to look for possible causes. House secretly has Foreman and Chase investigate Cuddy's house as well since Alfredo has been there for the past three weeks.
Cuddy and Cameron find a rat killed by a trap under Alfredo's dresser. The scars on Alfredo's hand must be rat bites. He has streptobacillus, which fits the symptoms perfectly. In Cuddy's bathroom, House notices a fuzzy, black aspergillus fungus on the pipes underneath the sink. Looking an x-ray, Cuddy agrees that fungal pneumonia is more likely. Cameron points out that the treatment for aspergillosis is amphotericin, which is hugely dangerous.
Stacy asks House to take it easy on Cuddy because she actually feels for patients. They're not just a puzzle to her. Meanwhile, Alfredo's little brother tells Cameron that Alfredo hasn't peed since yesterday afternoon. Cameron is concerned, and she immediately tells House that the amphotericin might have destroyed Alfredo's kidneys. Alfredo's mother overhears this and begins crying.
The team reviews what they know. The cause is not aspergillus nor rat bite fever. Alfredo tested negative for moraxella, nocradia and cryptococcus. DIC wouldn't cause a fever this high. House takes Alfredo's temperature and sees that the patient's right hand is starting to rot.
House wants to amputate the hand but Cuddy refuses to let that happen. She blames it on the medicine they gave him. If Alfredo loses that hand, he loses his jobs. House comments that this isn't medical thinking. House tells Stacy that Cuddy now agrees to the amputation and he begs for legal clearance. Cuddy tells Alfredo that it is necessary, and he tearfully agrees to the procedure.
During surgery, the fingers on the other hand start to turn purple. The team gathers afterwards with the news that Alfredo's O2 stats are down to 88 and his lungs are giving out. House wonders about endocarditis, which is an infected heart with little bacterial cauliflowers clinging to its valves. One may have broken off and traveled through the bloodstream to the right hand. Cuddy points out that they tested Alfredo for endocarditis and he was negative. House asks what infection causes pneumonia and culture-negative endocarditis.
Chase puts forward psittacosis, but Alfredo doesn't have any pet parrots. House orders a round of doxycycline, which Cuddy notes will make the clotting problems even worse. Cameron points out that, if House is wrong, Alfredo will lose his hands and feet. House and Cuddy barge into Alfredo's room. House asks the mother, in perfect Spanish, where Alfredo usually works on Saturday night. She says that he doesn't work. House knows that she's lying. House realizes that Alfredo works the cockfights on Saturday night.
Cuddy and Foreman head down to the warehouse district and find a cockfight. They see Alfredo's brother carrying cages of dead birds. Cuddy calls House with the news. House says he put Alfredo on the psittacosis meds as soon as she left. Cuddy later gives Alfredo the diagnosis. He's going to be okay.