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It starts with an armed robbery on a bus. The three robbers end up dead, the murderer manages to escape and the six witnesses on the bus seem unable to identify the fugitive. The agent Fran Garza and his partner - and ex-companion - Rebeca Quirós, in charge of the case, suspect that the witnesses are not telling the truth: the six claim they have not seen the face of the murderer, but everything indicates that they have made a pact of silence to protect the fugitive.