'How does it work?' Jack asks when he opens his present - a mobile phone. Later that night, Jack is a prisoner in a taxi in the empty streets of the dark city. He now tries his mobile phone for the first time. Can it save his life?'How does it work?' Jack asks when he opens his present - a mobile phone. Later that night, Jack is a prisoner in a taxi in the empty streets of the dark city. He now tries his mobile phone for the first time. Can it save his life?