A soaking wet Chinese man, Wu Zhe Lan, runs frantically through the streets of Boston searching for Ping-On Street. He finally locates the house he is looking for and urgently presses the intercom button. Another Chinese man, Ming Che, lets him in and tells him that he is the first to arrive. Wu Zhe Lan cries out that everyone else is dead. Ming Che tries to console him when he suddenly begins to cry out in pain. A tentacle begins to emerge from one of his nostrils!! Ming Che is unaffected and suddenly a multitude of thrashing tentacles begins to emerge from Wu Zhe Lan's mouth.
The Fringe team arrives at Dorchester Bay Inlet where a Chinese merchant ship has run ashore after catching fire. Many people died trying to swim to shore. At first, they believed the victims died of hypothermia until some people were found with large wormlike creatures with tentacles in their mouths. Walter examines the creature, and it appears to be similar to a parasite found in livestock. However he has never seen it this large before or in humans. He removes one from a body to take back to the lab to study. An FBI agent finds one woman still breathing. They rush to take her to the hospital before the organism kills her.
At the hospital, no worm is found inside Mei Lin's body. She informs Olivia that crewmen on the boat were giving others medicine for seasickness, but she did not take the medication. Mei Lin is worried about her husband and daughter who were on a boat that was scheduled to arrive 2 days after her.
Back at the lab, Astrid and Walter study one of the parasitic worms. Walter believes that humans were used as incubators for the worm togrow, as the time of gestation is equal to the time of transport. Olivia gets a phone call that the coast guard found a manifest on the sunken ship and has traced it to a local shipyard. They have someone in custody.
The man from the shipyard, Yang, sits in the interrogation room by himself. Peter recognizes the tattoos on his body; the man is a Triad gang member. Are the worms a new type of street drug? Before they can talk to him, Yang suddenly cuts his neck with a blade!!
Broyles debriefs Olivia and Peter on the information he has found on the Triad and its leader, John Hsu. He has set up shell companies to cover his criminal activities. They discover a woman, Elizabeth Jarvis, who transferred $500,000 to one of his companies, Beijing Executive Construction.
Peter and Olivia arrive at Elizabeth's home and are greeted by her son, Matt. Elizabeth reveals that her attorney advised her that there was money to be made in the company. Peter's attention is caught by an abundance of hand sanitizer and hermetically sealed windows.
After Walter is inadvertently bitten by one of the worms, he discovers that his white blood cell count is extremely high and he has new antibodies. The worm is not a narcotic...it's a medicine.
Walter visits three herbalists in Chinatown who sell hookworms similar to the ones found on the victims, but smaller. He spots Astrid following him and becomes angry. He finally relents and lets her come with him to the shop. They arrive at Ming Che's shop, and Walter tells him that he has a four-foot hookworm. After Walter leaves, Ming Che makes a phone call to another man who begins to follow Walter and Astrid. Walter wanders off when he becomes distracted by a nearby shop- Astrid is unable to find him.
Peter returns to the Jarvis' home to talk to Matt. He reveals to Peter that his mom isn't the one who needs the medicine from the worm... he is. Matt suffers from a rare immune deficiency disorder in which he doesn't have enough white blood cells to fight off infection. The powder from a gland in the hookworm is the only thing keeping him alive. His next treatment is scheduled in 2 days...the same day as the next boat's arrival.
Walter begins to call various numbers unable to remember the correct sequence of Peter's phone number. A Chinese woman empathizes with him and takes him back to her apartment.
Peter and Olivia return to the lab and find Astrid knocked out on the floor. The hookworm is gone. Peter receives a phone call from Walter and leaves to get him.
The boat carrying Mae Lin's family has finally arrived. The FBI team arrives but they are too late. All of the immigrants are gone.
Peter retrieves Walter and finds out that Walter told one herbalist shop that he had a four-foot hookworm. Peter believes this is the place responsible for following Astrid back to the lab and stealing the worm. They pull up to the shop and discover a large number of Chinese exiting a van. Peter calls Olivia to inform her, and she assembles a team to come over.
Our team is able to save the immigrants from Ming Che. They take them to the hospital where their prognosis is hopeful. The state department has granted them political asylum. Mae Lin's husband and daughter are both safe.
Walter tells Peter that he does not want to be treated like a child anymore. He has been out of the institution for nearly a year and is just beginning his journey to being whole. He still fears there will be a time when he will get lost, so he has implanted a tracking device in his neck. He gives Peter the transponder to keep track of him.