1. The episode opens with a chase scene: police officer Joe Luria (Scott Michael Campbell) is pursuing a suspect named Baby Shoes (Chioke Dmachi). It quickly becomes apparent that things are not quite right with the cop. What is his strange symptom? He's very happy and can't stop laughing -- even after he's shot. His left arm is twitching uncontrollably. He has short-term memory loss; for example, he reads Baby Shoes the Miranda warning twice. He speaks more and more slowly as the scene unfolds, finally passing out.

2. As the diagnostic medicine team starts brainstorming about the police officer's symptoms, it's clear that there's still some lingering tension between Cameron and Foreman over events a few episodes previously. What is their fight about? They disagreed about how to advise a woman who wanted to donate part of her liver to her girlfriend. Foreman published an article about a case that Cameron had also written up for publication. Foreman laughed when Chase joked that Cameron was only good for testing bacteria. Cameron is angry about the decisions Foreman made when Cuddy put him in charge of the department.

3. Temporarily stumped as to the cause of Joe's condition (now causing involuntary muscle spasms in his arms) -- and unable to do an MRI due to the metallic bullet fragments still lodged in his brain -- House employs his usual fallback plan: he instructs Foreman to break into the patient's apartment and get samples of anything suspicious. What is unusual about the apartment? The apartment is spotless except for the kitchen, where Foreman counts 14 distinct genuses of mold and finds evidence of rats. The apartment is exceptionally filthy, filled with rotting food and even a bucket of pigeon droppings. Nothing else is unusual. Not only is the apartment filthy, but it also contains an illicit greenhouse of marijuana plants. Not only is the apartment filthy, but it also contains exotic pets not strictly legal under city law, including a caged tiger.

4. The team attempts to show Joe his improving chest X-rays -- and in the process they realize he's developed a new and disturbing symptom. What is it? Uncontrollable weeping Glaucoma Anton's blindness Ocular bleeding

5. More trouble arises when Foreman starts to display the police officer's earliest symptom. What is House's first clue that something isn't right? Foreman's hand shakes so much that he has trouble performing simple procedures. Foreman collapses in front of the whiteboard. Foreman repeats the patient's latest test results to House -- four times. Foreman laughs inappropriately when House shoots a corpse in the head.

6. Joe's mystery illness has now infected two people: himself and Foreman. Everyone fears an epidemic. Joe and Foreman are confined to the same isolation ward; the apartment is sealed off as a biohazard area. Cameron wants to go back to the apartment to get more samples and perhaps to solve the mystery, but House won't let her -- so a desperate Foreman tries an unorthodox way of persuading her to do it anyway. What does he do? He tears a gash in her biohazard suit. He stabs her with a contaminated needle. He lies that he saw a group of children near the apartment before it was sealed off. He lies that he was infected by a needle stick, and not by his visit to the apartment.

7. After a few heart-to-heart chats with Foreman and one heartrending new symptom -- uncontrollable pain that persists even in a coma -- the police officer finally dies. House is ecstatic: surely the autopsy will reveal the nature of the infection! It turns out, however, that the hospital can't perform an autopsy. Why not? The body is mistakenly burned as an epidemic-prevention measure before the autopsy can be done. An accident in the morgue makes the autopsy equipment unusable. Joe's family arrives and insists that autopsies are against their religious beliefs. To avert an epidemic, health regulations require that the CDC handle the autopsy.

8. Comparing Foreman's charts to Joe's, House realizes that the mystery illness is progressing much faster in Foreman than it did in Joe. Why? Joe's exposure was slow and happened over a long time, whereas Foreman's exposure was quick and acute. Foreman's race makes him more susceptible to this particular illness. Joe had Legionnaire's disease, and Foreman doesn't. Joe's drug use changed pathways in his brain, making him slightly less susceptible.

9. Eventually, House gives Foreman a cocktail of pills to treat every infection he can think of, and for a time this reverses the progress of the mystery illness. Unfortunately, the drugs start to threaten Foreman's pancreas, and he has to be taken off them -- and then his decline is swift. Soon he'll have to be put into a coma to help manage the pain, but someone will have to make his decisions. To whom does Foreman give medical power of attorney? Cameron His father House Chase

10. At the end of the episode, the situation is desperate. House tours Joe's apartment one last time, hoping to find the answer while the dangerous brain biopsy can still be avoided. What turns out to be the cause of the mystery illness? Naegleria fowleri, an ameba that had contaminated the water in Joe's greenhouse sprinkler system Yersinia pestis, the plague bacterium, carried by the rats in Joe's filthy apartment Cryptococcus bacteria that had contaminated Joe's fertilizer A tapeworm -- contained in Joe's ham sandwiches -- that made its way to the brain