Two brothers, Prosper and Boniface Hartleib, run away to Venice and are taken in by a group of street children who are led by a proud orphan named Scipio, AKA "The Thief Lord." The runaway boys' aunt and uncle figure out where they are and hire a detective, Victor Getz, to find them. While investigating the thief gang, Getz discovers that Scipio is actually the son of a successful doctor, Dr. M…