 The Mitchell family (the father, Brian, and his children Mike and Sandra), goes to the big city for to beginning a new life until what something goes bad when the three are surrounded in a jewel robbery, more concretely emeralds and diamonds; the police search of robbed jewels makes damage in the lives of Sandra and Mike, to the time that the emeralds and diamonds follow without appearing; Brian is finally arrested like first suspect of the thieve, and the true thieves narrow the danger around Sandra; in a persecution through the dark streets, an unexpected ally appears in one biker BMX to guide Sandra and Mike by the return way to safe place; while Mike and its friend Lee try to hacker a government computer, an intelligent tramp attracts Sandra towards the danger; behind a threatening visit of the mysterious figure behind the robbery of jewels, Sandra decides to take to the thieves in its own game; after hacker the computer, "Mr. Mysterious" is unmasked and they are put after the track of the test that he will identify to the rest of the thieves; that way the action converges in jewels and all the enigmas are solved, arriving the final confrontation between the Mitchell, the thieves and the mysterious figure of the black biker in his black motorcycle that it has persecuted to them from the beginning of the plot.