Teen-aged Leonardo Da Vinci is an apprentice to the painter Andrea Del Verrochio and his friends include the super-clever Macchiavelli and Lorenzo,son of scheming Piero De Medici. Leonardo is impressed by the work of Tomasso, a pavement artist and persuades Verrochio to take him on as another student,which he does. When Tom is caught trying to take Leonardo's notebook the boys are in for a surprise. Tom is a girl called Lisa,in disguise in order to be allowed to paint.
Aware of Leonardo's budding genius Piero steals his notebook but finds it impossible to understand because all the information for his designs are written in code. He brings in Maths professor Pico to decipher it but even he is foiled as Leonardo,at great risk to himself,eventually retrieves his notebook.
Leonardo has perfected a pair of giant wings,enabling him to fly but Macchiavelli has fallen foul of fat,sleazy thief Rizzo,who threatens him with prison unless he can have the wings for himself. Eventually the wings end up with Piero,who forces Rizzo to test them. But will they take the weight of a man twice as heavy as Leonardo?
Leonardo and Tom are commissioned to paint a portrait of young bride-to-be Petronella,who is marrying thuggish,dishonest money lender Lucio solely to free her father from being in his debt. Macchiavelli recognizes Lucio as a man who hurt him when he was a child and,with the artists' help,concocts a plan playing to Lucio's greed by making him pay 100,000 florins for what they have told him is the alchemist's stone,to turn lead into gold. Having parted him from his money they then literally frame him for stealing a painting,freeing Petronella - who guesses 'Tom's' secret but says nothing.
Lorenzo's spoilt cousin Valentina arrives and Leonardo is smitten by her. She also falls for him but then transfers her affections to Tom,unaware that 'he' is Lisa in disguise as girls are not allowed to be art students. When Valentina discovers the truth she sets out to expose Lisa. Fortunately Leonardo's latest invention, a bicycle powered by explosives,is able to head her off before she can tell any tales.
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.
After a Swiss clock-maker bringing a pocket watch to Piero drowns Leonardo finds the watch and discovers that it is magic and that it runs backwards,enabling the user to travel back in time. Machiavelli makes a copy which he tries to auction and this comes in useful when a gang of heavies pursue Leonardo for the real thing,which he is able to return to its maker's mother so that she can see her son again.
Lorenzo's uncle,the duke,sets a competition to find Florence's finest painter and cocky Michelangelo taunts Leonardo that he cannot beat him so Machiavelli enlists Lorenzo's help in tricking Michelangelo into painting the duke's least preferred topic,angels and cherubs. Leonardo,however,is annoyed that he is expected to collude in cheating and deliberately erases the smile from the teen-aged version of La Gioconda which he painted using Lisa as his model,thus allowing her, as 'Tomaszo' to win.
Lisa's mother arrives in Florence to find her daughter and take her home for an arranged marriage, unaware of her new identity and profession. In order to put her mother off,Lisa tells her that she is already married and presents Machiavelli in a charade where they play at being husband and wife. Mother is not fooled for one moment but will her appreciation of Lisa's burning desire to be an artist be enough to let her stay and continue her work?
Piero hosts a party for the celebrated charioteer Giovanni Salvatore which is gate-crashed by Lisa and Leonardo,posing as staff,and Machiavelli,passing himself off as Count Lampedusa. Piero sees through his disguise and has him imprisoned but Leonardo saves him thanks to a couple of his recent inventions. However the false count has persuaded Giovanni to give up his sport to undertake charity work - not a popular decision among his Florentine fan base.
After Piero has coerced 'Tom' into stealing Leonardo's notebook Leonardo and Machiavelli set out to recover it,planting a copy with blank pages. Meanwhile Lorenzo is temporarily held to ransom by Belladonna, the Bandit Queen of Florence,and Lisa,who has followed Leonardo,seized by Piero as an accomplice. Though the boys succeed in retrieving Lisa and the book,as well as seeing off Belladonna, they are aware that Piero now knows that Verrochio is illegally employing a girl as a painter - but unaware that he has made a copy of the notebook.
Piero summons Leonardo to his palace and suggests that,as both are 'men of vision',they should work together to produce one of the inventions in Leonardo's notebook. It is a toy but Machiavelli is led to believe that it is a bomb,with which Piero intends to kill the duke of Florence at his birthday party. Leonardo humiliates himself when the invention turns out to be the harmless toy and not the bomb about which he warns the duke. Piero has,of course,kept the real bomb for himself.
A robot,designed by Leonardo but recreated by Piero as a fire-breathing demon,is on the loose in Florence until Piero,who has orchestrated its retreat, is declared a hero and asked to take over power from the duke. At last Leonardo appreciates that this is the culmination of Piero's theft of his note-book as a means to rule Florence. Accordingly he makes sure that during the 'demon's' next outing Piero is discredited and the duke reinstated. This however alienates him from dim Lorenzo,who cannot see his father's villainy.