The mastermind villain Le Bled shows up at Narutaki's home and suggests a competition: if Narutaki can find the 3 great treasures of Steam City in an 18 hour period, Le Bled offers to surrender to police, but if he cannot, Narutaki agrees to stay out of Le Bled's affairs. The competition becomes even more intense once Narutaki discovers that the treasures are in fact bombs and are set to go off at the deadline...
