Derek and Richard wait outside for a special patient with a serious problem. Archer Montgomery, world famous neurologist and brother to our very own Addison Montgomery is suffering from continuous, unrelenting, dangerous seizures. Addison, unwilling to believe her brother's condition is fatal had Archer airlifted to Seattle Grace and has asked Derek to save him. Archer's got neurocystercercosis or parasites in his brain. Is it too late for Derek to help him?

Unlike the common cold, neurocystercercosis isn't an air born infection, it is a fecal, oral disease, meaning it's shed in the bowel movements of a host and must be ingested by a new host in order to cause an infection. When Archer visited Mexico, he ate unwashed fresh fruit. Unfortunately, crops from undeveloped countries are often irrigated with water with fecal contamination and Archer ate tapeworm larvae.

The larvae traveled to the intestines where it hatched. Then were absorbed into the bloodstream. They traveled through the circulatory system where they were able to penetrate the not-easy-to-get-through blood-brain barrier and arrived in the brain. Here, they found a good place to live, the third ventricle.

The third ventricle is located deep, deep in the brain, between the two hemispheres. It's chamber with a constant flow of cerebral spinal fluid (CSF) flowing through it. It's very important that the stream remain flowing, because there's nowhere to store excess CSF fluid. If there is a back-up of the fluid, the third ventricle swells, putting pressure on the brain stem, which controls basic functions like breathing and the heartbeat.

There's no easy way to get to the third ventricle, which is why Archer has been adamantly against surgery. Derek concurs, at first...

As Derek looks at the pictures of Archer's affliction he formulates a plan. If Derek were to use an endoscope, he could thread a small tube through the brain into the third ventricle and feed the necessary tools through this tube. He will need something to pierce the cysts and a vacuum instrument to remove the fluid and the worm quickly. If he does this one by one, there is a chance he could remove all of the cysts and all of the worms living in them, waiting to hatch.

Just as Derek is about to finish the surgery, one of the cysts bursts and a tiny little worm escapes and swims through the ventricle, blocking the hole that the CSF drains from. This causes Archer to go into cardiac arrest (or to code). The natural instinct of everyone in the OR is to resuscitate Archer's heart, but, unless Derek can relieve the pressure that the buildup of CSF fluid is putting on the brain stem, they will not be able to start the heart. If Derek can't capture that worm, no amount of shocking Archer's heart is going to bring him back. Luckily Derek knows this. He quiets everyone and focuses. Sure enough, Derek is able to catch the renegade worm and Archer's heart begins to beat, just like Derek said it would.