In Season 1, a serial killer preys on men, Carol tries to catch a stalker plaguing a celebrity couple and an abduction and murder cause professional tension between Tony and Don.
In Season 2, Tony persuades the police to reopen the case of a convicted child-killer, building work unearths grisly remains and an imprisoned gangster masterminds a murder.
In Season 3, a boy's body is discovered in a warehouse, one of Tony's PhD students is suspected of murder and Carol contends with a sniper spreading terror throughout Bradfield.
In Season 4, Carol is replaced by new detective Alex Fielding, a prostitute is murdered and Tony investigates a series of deaths resembling the martyrdoms of Christian saints.
In Season 5, Tony is called in to help investigate the abduction of an 11-year-old girl and the murder of two youngsters in ritual slayings leads the team to investigate black magic.
In Season 6, the dismembered remains of a Kurdish woman suggest an honour killing has taken place, Tony is suspected of murder and cannibal killer Michael reveals he is planning to escape.