Having returned from Titan, Dejah reunites with her Grandfather and Father and finds that a Criminal Underworld has gotten a foothold in Helium led by the enigma "MORTUS." In order to discover Mortus true identity and bring down his organization, Dejah and a notorious Weapons Master assume different identities and infiltrate Barsoom's criminal underworld where they encounter assassins, gangsters, and a vile world of corruption and deceit that Dejah never knew existed.