During the fifth season, the Syndicate discovered that Covarrubias had betrayed them and was providing information to Mulder. Covarrubias was infected with black oil during her betrayal of the Syndicate, and Syndicate scientists used her to test a vaccine they had been working to create. While the Syndicate-developed vaccine proves ineffective, Covarrubias' infection is ultimately cured by an effective vaccine stolen from a Russian shadow-government group by Alex Krycek. In the following season, Covarrubias is discovered by FBI agent Jeffrey Spender (Chris Owens) at a decontamination chamber. She begs him to help her escape the facility, addressing him by name as well as giving him information about the whereabouts of his mother, Cassandra. Alex Krycek (Nicholas Lea), a former Syndicate agent now acting alone, is also present at the facility. He declines to help the pair, and leaves Covarrubias for dead.