The authors have undoubtedly taken considerable liberties with the career of Leonardo da Vinci, but it really doesn't matter since this is in essence an uncomplicated 15th century action-adventure which proceeds from Leonardo's contribution to the art of ballistics. Much of the story takes place outside the Roman-held bastion of Castelmonte, besieged by Lorenzo de Medici, for whom Leonardo serves as military engineer. Between reconnaissance missions at the battlements, Leonardo is out in a field experimenting with arrows and guns -- to invent a new method of firing by mathematical calculation. He visits Rome, is set upon by assassins, and has an affair with -- and this is truly out of line -- Bianca, cousin of Lorenzo. However, in spite of the fabrications, the authors have given Medicis' warfare a blistering verisimilitude and the tale moves with the speed of Leonardo's drawing (which he does herein with both hands at once). If not taken too seriously, a satisfyingly noisy cannonade.