Mary is a competitive diver. She had a rash, which she had attributed to her new bathing suit. She also had a stiff neck. She travels with her coach and the rest of her teammates to compete. Sometime before the events of the episode, Mary was asked by a boy to have intercourse with her. She actually agreed to his request, and they both had penetrative [underage] sex together. However, because neither wore protection as her partner ejaculated in her uterus, she unknowingly became pregnant.
Mary came to the hospital along with several hundred other individuals due to a meningitis outbreak at a diving meet attended by 2,500 people. All the area hospitals in Princeton were overwhelmed and Princeton-Plainsboro Teaching Hospital was responsible for examining over 800 people for signs of the disease.
Dr. House was in the clinic examining people that were at the pool when Mary was assigned to him. She had a fever, and Dr. House asked her if she had a rash. She showed him her rash and told him that it was from her new bathing suit and she had had it for a week. He asked if her neck hurt, and Mary claimed she pulled it trying to do a three-and-a-half tuck at the diving meet. Her parents were in Chicago and she was there with her coach. However, her neck hurt when she moved her head side-to-side but not when she moved it up-and-down.
House got his team together. Dr. Chase thought it might be systemic, but Dr. Foreman thought it was just meningitis. However, if the patient was telling the truth about having the rash for a week, meningitis would have killed her by now. Dr. House told Dr. Cuddy about Mary, Cuddy thought it was meningitis, but House reminded her that meningitis restricts up and down movement because of pus in the spinal column, not just side-to-side movement. Cuddy gave them one hour to perform additional tests. House told Dr. Foreman to get a lumbar puncture and assigned Dr. Chase to research all the known causes of neck pain. However, he also ordered rifampicin in case it was just menigitis.
Dr. Foreman asked Nurse Previn for a bed so he could perform the lumbar puncture, but she sent him to the back of the line and told him it would take at least four hours.
Foreman had to do the lumbar puncture on a gurney in the hallway due to the epidemic. Dr. Foreman administered novocaine and performed the LP with her coach's assistance. Dr. Chase was still on the letter "A" for his research. However a while later other people needed the gurney so she was placed on a couch despite the fact she was not in condition to be moved. She was dizzy and had a headache, which Dr. Foreman put down to her being moved. Luckily, the LP showed no meningitis or other infection. However, because they could not explain the fever, rash and neck pain, they had to admit her. Mary started feeling what she thought were tears, saw they were red, and she thought that her eye was bleeding. Dr. Foreman told her that the antibiotic they gave her in case she had meningitis had made her tears turn reddish. However, on further examination, he realized that her mouth was bleeding.
Dr. Chase and Dr. Foreman decided to perform an endoscopy to see where the blood came from. Dr. Chase anesthetized the patient's throat with a local anesthetic and Dr. Foreman administered a sedative. However, the endoscopy showed no bleeding from the throat to the duodenum despite the fact there was over a tablespoon of blood. Given that they could not examine her intestines with the endoscope, they gave the patient another small camera to swallow which would pass through her entire digestive tract. Dr. House examined the pictures and found a small swollen blood vessel. Dr. Foreman thought it might be a precursive intestinal intussusception. At this point Dr. Cuddy arrived and demanded that they return to examining meningitis patients as two more buses had arrived and even if the patient had intestinal bleeding, she could wait.
The team attempted to continue the differential while treating menigitis patients. Dr. Foreman suggested stomach cancer, but the patient had no abdominal pain. Although the tests showed no infection, Dr. Foreman thought the lab, being so busy, may have screwed up the results. Dr. Chase thought the neck pain could be a sign of bone cancer, which would also account for the rash and fever. Dr. House ordered Dr. Foreman to use his and Chase's break to do a bone marrow biopsy.
Because of the epidemic, Nurse Previn refused to give Dr. Foreman a bed to perform the biopsy. As a result Dr. Foreman was forced to do the biopsy in the morgue because of the epidemic.
Some of Mary's friends came to see her. Dr. Foreman asked them to leave for a minute, but Mary told him that if it's good news he could tells them. Foreman told them that they were pretty sure it wasn't cancer, but they still couldn't release her because of her symptoms. Suddenly, she had an absence seizure. Dr. Foreman ordered 2mg of adivan stat. He examined her pupils, which did not respond to light.
Dr. Foreman was sure it was an absence seizure - she was totally unresponsive and unaware of her surroundings. Her EEG showed that she was having multiple seizures and they were increasing in frequency - five in the last half hour. This showed that whatever she had, it was in her brain and was getting worse. Dr. Chase thought it might be barbituate withdrawal, but Dr. Foreman noted that she was constantly tested for drugs at her diving meets, which probably ruled out any drug at all as the cause of her symptoms. Dr. House thought it might be a bleed in her brain and Dr. Chase suggested rat poison. Dr. Foreman was incredulous about her having been exposed to it, but Dr. House suggested she might have been deliberately poisoned. Dr. House told them to do a CT scan and check for intercranial bleeding. Dr. Foreman reminded Dr. House that radiology was full of meningitis patients. Dr. House told them that Mary would be dead in eight hours if it was an intracranial bleed, but Dr. Foreman reminded him they had no proof that this is what was wrong with her and that meningitis patients will also be dead without an immediate CT scan. Dr. Chase told them about an old professor of his who specialized in transcranial ultrasound. Dr. House tells them to do that, but that will only work if there is a lot of bleeding. However, Dr. House instructed Dr. Foreman to do the ultrasound and told Dr. Chase to go back to his research.
Dr. Foreman performed the ultrasound. Dr. Chase continued to research all the known causes of neck pain. Mary was still having absence seizures.
Dr. House asked Dr. Cuddy for an operating room and a neurosurgeon. Cuddy said no, but House told her about the temporal lobe bleeding, and Dr. Cuddy agreed to give him the OR and the neurosurgeon in ten minutes.
They did the surgery to relieve the intracranial pressure. Mary's parents arrived at the hospital and met with Dr. Foreman. Mary's father asked if she was alright, Foreman told him that the operation went well. The intercranial pressure had been relieved and the swelling was already going down. Mary's mother asked what caused it, and Dr. Foreman told her that they still didn't know although they had ruled out trauma.
They had ruled out a tumor, bone cancer and toxins. Dr. Foreman noted kidney failure could cause all the symptoms and it might be a genetic kidney disorder. However, there was no blood in her urine. Still without an answer, Dr. House asked what else they did know about the patient. They all noted that she spends a lot of time in pools, she's 12, and she travels a lot but never out of the country. Dr. House was sure that they were missing something. Dr. Chase thought maybe she was adopted, throwing off her medical history, but Dr. House noted several features that she had in common with her parents. Dr. Foreman thought it might be an allergy, but although this would explain the rash and paint, it wouldn't explain the bleeding and seizures. Suddenly, Dr. House notes that she has a lot of balloons. He wondered if the rash wasn't really a rash. He asked who gave her the balloons, and Dr. Foreman told him that it was some girls on her team, but none of them were sick. Dr. House asked about the guys on her team, but none of them had visited her despite the fact that she's cute, nice and a great diver. Dr. Foreman told House that the youngest guy on her team is 16 and implied that they wouldn't be interested in her because of her age. However, Dr. House thinks that her male teammates are avoiding her. He asked if there were any cell fragments in her blood smears, and there were none - her red blood cells were intact. Dr. House ordered Dr. Chase to repeat the test, which showed shredded red blood cells and that the rash was actually blood bleeding into her skin. Chase suggested Thrombotic thrombocytopenic purpura, which would account for her symptoms. However, Dr. Foreman wondered what set it off because she had no sign of e. coli in her system and she was not in menopause. However, Dr. House reminded him that there was one other possible cause.
Dr. House went to see Mary, he told her that pregnancy causes all kinds of chemical and biological changes. He performs an ultrasound of her uterus and finds that she's pregnant. This set off the T.T.P. which caused clots in her brain and kidneys that shred the blood cells. House thought that perhaps one of the boys had taken advantage of her with alcohol, but Mary told him that she agreed to let a boy have sex with her. Dr. House told her that they had to give her plasmapheresis to clean out the damaged blood. He also told her that they would need to terminate the pregnancy. Mary asked if House had to tell her parents. House told her that under New Jersey law, she decides whether or not to tell her parents and could make her own decision about the abortion.
Dr. House informed the patients that she had T.T.P. and that she would fully recover and could go home in a few days after minor abdominal surgery. However, he would not go into details about it and cut off the parents when they pressed him on it.
Mary underwent the abortion procedure and responded well to the plasmapheresis, with prognosis for a full recovery. She asked to see her parents and told them about the pregnancy. They embraced her.