The, film opens with a fantasy sequence in which Johnny English (Rowan Atkinson), an inept British Intelligence agent, is "Agent One". He sneaks into a building, distracts two guard dogs with toys, knocks out two guards and seduces a woman who threatens him. He is awakened from his fantasy, just as he is about to kiss the woman, by his sidekick, Angus Bough (Ben Miller). After being assured that English has checked the submarine hatch codes personally, the real Agent One (Greg Wise) leaves on a mission. The audience then learn that Agent One died in action when his submarine hatch "failed to open". A bomb then wipes out Britain's remaining agents, all of whom were attending the funeral of Agent One, leaving only English. Nobody notices the hearse, which sped from the scene minutes earlier.
Before his death, Agent One was investigating a plot to steal the Crown Jewels. Together with Bough, English takes over the case. While investigating, English becomes attracted to a mysterious woman, Lorna Campbell (Natalie Imbruglia), whom he meets at the unveiling of the newly restored Crown Jewels, where English is in charge of the security. The power to the room is cut, and English accidentally knocks out the chief of security, before pretending to fight a criminal in another room in an attempt to cover up this fact. Later, Bough and English follow a tunnel and find the Jewels, but fail to stop the thieves after English accidentally ejects the magazine from his pistol. English chases their car, a hearse, but accidentally ends up trailing the wrong hearse after being stopped by a red light. Convinced the burial party he discovers is an act, he accuses the mourners and the priest before realizing his mistake after another man told English he was the hearse driver. Bough rescues him by pretending that English is an escaped asylum inmate.