Still in the hospital, the newborn Hartig daughter spits up and the mother is concerned because the baby hasn't eaten anything yet. The baby suffers a seizure.
Later, a nurse who was in the room recounts the incident to another doctor in the lounge. She discusses the baby's bowel obstruction. House overhears their chat and quickly leaves.
House presents Baby Hartig to his staff as Exhibit A. Exhibit B is Baby Hausen, another newborn who is also ill. House thinks an infection is spreading throughout the hospital, but Dr. Cuddy isn't buying it.
House tours his doctors in the maternity ward to check the twelve newborns in the hospital. Nothing. But they do find one more baby upstairs with a sudden fever and similar symptoms.
House and crew discuss three sick babies and the symptoms. With a spike in fever and low blood pressure, these children could be dead in one day. The group thinks it might be a bacterial infection.
Since there's no time to wait for test results, House orders the treatments to be started. Each baby gets an MRI. Nothing shows up on the scan, so the doctors continue administering two antibacterials. One of them starts causing the kidneys to shut down in two of the three babies.
But which one?
House says there's no point in guessing, so take Baby Hartig off the Astrianam medication and Baby Chin-Lopino off the Vincomiacin.
Dr. Cuddy and a hospital administration refuse to allow House to change the treatments without informing the parents. He pleads that this experiment will save at least six more babies, so Cuddy gives him the green light.
Later, the Chin-Lopino baby's health begins to worsen with a falling heartrate and blood pressure. The doctors rush in and try to shock the baby back to life. The baby dies. The Astrianam doesn't work. House instructs his staff to cover the rest of the babies with Vincomiacin.
Dr. Chase informs the team that the Vincomiacin isn't working either as the Hartig baby is getting worse. Perhaps it isn't a bacterial infection.
House performs an autopsy on Baby Chin-Lopino and devises a theory that it is a virus and not a bacteria that is affecting the babies' hearts.
Dr. Foreman complains that it could be a 1000 viruses. However, with the amount of blood in the babies' bodies, they can only run five or six tests. So House tries to narrow down the list of possibilities, and end up with eight. That is still too many with a limited amount of blood to be drawn.
Chase gets to work. House also has Cuddy take blood from the one healthy newborn in the hospital to use as a control group.
The sick babies all test positive for Echo virus 11, CMV and Parvo virus B19. The healthy baby tested positive for Echo and CMV antibodies. House realizes that these infants still have their mothers' blood and immune systems, so he orders a test on the mothers to see what they have antibodies for. Whatever the women are missing is what is killing their kids.
After more testing, the doctors settle on Echo virus 11. They have an experimental anti-virus in the hospital and give it a shot.
Chase and Foreman bring good news to the Hartigs. Their baby is recovering. All of the babies are recovering.
That night, House observes an elderly maternity ward nurse coughing and wiping her nose as she pushes around a cart of baby toys and blankets.