Piero has acquired a 'lightning box',which gives out electric charges and which he plans to exhibit. A curious Leonardo 'borrows' it to study but a devious associate of Machiavelli,Carlo,steals it after giving Machiavelli a hard luck story. Leonardo makes a replica as a temporary replacement,almost getting caught putting it in place, but when Machiavelli learns that Carlo has duped him he helps retrieve the real lightning box before Piero detects any difference.