The Wager between Heaven and Hell is over. Heaven won. As a result of this, all demons have been returned to Hell and the angels who have spent the duration of The Wager on Earth are given the option of returning home. Harmony is one angel who has enjoyed her time on Earth and is in no rush to leave. She feels that angels still have a purpose on Earth; to help mankind. Whilst helping one particular mortal, Harmony sets off a series of events that leads her to discover that a number of demons who have not given up the battle for claiming Earth. Dylan, along with the now-exiled Bethany, has utilised a demon-created virus to achieve the first successful cases of possession and have brought through a number of fellow demons into mortal bodies. Their task, however, is to be hindered by the research of a vaccination against the newly discovered virus that is beginning to appear within the city. They must stop the research so as to allow further demon possessions to be possible. Still affected by the death of a close colleague and friend, Detectives Alex Carter and Richard Dwyer are called to the scene of home invasion to investigate the death of a leading medical researcher, a man who was loved and respected by the people he worked. This leaves the mystery as to who would torture and kill a man with no apparent enemies. As the case unfolds, different paths will cross and secrets will be revealed.