In Pixar's Cars 2, the British spy car who partners with Mater during the international investigation is Finn McMissile.
Finn McMissile is an experienced British secret agent voiced by Michael Caine. He first mistakes Mater for an American agent and draws him into the investigation surrounding the World Grand Prix. Their partnership becomes one of the film's main comic and action-driven relationships.
Finn investigates the sabotage affecting cars that use Allinol. He works with Holley Shiftwell, a younger British agent, while Mater contributes accidental observations that the professionals initially overlook. The story deliberately contrasts Finn's polished spy manner with Mater's informal behavior.
Finn is not the film's villain. That role belongs to Miles Axlerod, who organizes the conspiracy behind the fuel plot. Holley Shiftwell is Finn's fellow agent, not his partner in the sense of being the character who first recruits Mater.