S8E18 · Vienen

Simon de la Cruz, a worker on an oil platform in the Gulf of Mexico, fatally stabs fellow crew member Ed Dell, the radio operator, who’s been infected with the black oil. He then starts destroying the platform's radio equipment but is killed by Bo Taylor, whose body then begins to glow.

At FBI headquarters, Special Agent Fox Mulder (David Duchovny) tells Special Agent John Doggett (Robert Patrick) about the murder and explains that ninety percent of de la Cruz's body was covered with apparent radiation burns. Galpex Petroleum, the platform's owner, officially attributes the burns to an explosion, but Mulder suspects the involvement of extraterrestrial " black oil ". Mulder and Doggett meet Galpex's vice-president, Martin Ortega (Miguel Sandoval), who tells them that the company has discovered a large oil reserve in the Gulf of Mexico. Deputy Director Alvin Kersh (James Pickens, Jr.) sends Doggett to the Gulf to investigate, but Mulder is already present when Doggett arrives.

Doggett also arrives with the Galpex Orpheus’ new communications officer named Yuri, who after repairing the damaged communications system is immediately infected with the black oil by chief Bo Taylor. The agents meet Taylor, who claims de la Cruz tried to blow up the platform.

Meanwhile, when performing an autopsy on de la Cruz, Special Agent Dana Scully (Gillian Anderson) finds black oil in his skull—curiously, the oil is dead and seems to have been irradiated. In the interim, Doggett and Mulder find proof of black oil and quarantine the platform, but they soon learn that de la Cruz's friend Diego Garza is missing. Ortega threatens to bring back the crew unless the agents can provide proof of an infection. While Doggett and Mulder search for Garza, they discover that somebody has set fire to the communications room. As the agents tackle the fire, Garza attacks Doggett and renders him unconscious. When he awakens, Garza, now mentally unstable, cuts his arm to check for the presence of black oil, and warns Doggett in Spanish that "they're coming".

Meanwhile, an annoyed Kersh tells Scully that he is lifting the quarantine of the platform, which she is forced to reluctantly obey. Scully then realizes that de la Cruz is immune to the black oil due to his indigenous Mexican heritage: Because of this, he suffered from radiation burns instead of infection. After talking to Garza, Doggett leaves to find Mulder but is attacked by Taylor. Mulder arrives and overpowers Taylor, and the agents barricade themselves in the communication room. As the infected oil rig workers begin sieging the communications room, Mulder and Doggett attempt to relay a message while the platform's crew attack the door.

Scully receives the message and tells them that Kersh has broken the quarantine. Mulder destroys the platform's radio so that the infected crew cannot communicate with the aliens. Suddenly, the crewmen stop their attack and decide to sabotage the platform to kill Mulder and Doggett. This forces Doggett and Mulder to jump off before it is destroyed. They are rescued by the helicopters Kersh has sent to break the quarantine. Later, Mulder informs Doggett that he has been dismissed from the FBI.