Prelude is the 7th episode of Season 3 of Alias and the 51st episode overall. Sydney accompanies Sloane on a Covenant assignment to steal the operating system for a microwave laser from the Chinese Defense Minister's office. Meanwhile, Vaughn and Lauren go to Mexico to meet Javier Perez, one of Simon Walker's former associates, who was captured by Mexican police and who claims to have information about Lazarey's murder.