In the mid 1970s, Kiwi charmer Terry Clark and "Aussie" Bob Trimbole form a deadly alliance that will change the face of Australian crime forever.

Anti-drugs campaigner Donald Mackay makes deadly enemies with the Griffith mafia and corrupt NSW police. Melbourne crim Ray Chuck plans Australia's most audacious heist - the Great Bookie Robbery.

A naive young Kiwi, Allison Dine, is swept off her feet by Terry Clark, becoming his lover, and most inventive drug courier.

Melbourne standover men Brian and Les Kane have ventured into unfamiliar territory by providing protection for Bob Trimbole's Melbourne heroin dealers. But things turn sour when dealer Wayne Robb is robbed of $200,000 cash on the Kane's turf. The Kane's suspect it was Vinnie Mikkelsen and Laurie Prendergast, two of Ray Chuck's mates from the Great Bookie Robbery.

Brian Kane plans Australia's most audacious gangland murder to avenge the death of his brother Les. Meanwhile, Ray Chuck forms an alliance with Mark "Chopper" Read in a Melbourne jail. Also, aspiring hitman Chris Flannery finally gets his big break and Terry's growing drug empire is under threat from problems in Australia and Singapore.

When Terry is arrested after a boisterous party in a Brisbane luxury hotel, its an old New Zealand criminal charge that sees him extradited for trial in his home country. There he meets the striking Karen Soich, a member of his legal team, and its quickly clear that the attraction is mutual. With Terry gone temporarily, Allison takes the reins in Australia, organising new couriers to ensure business stays booming. Meanwhile, trusted drug couriers Doug and Isabel Wilson use Terrys absence to clear their consciences and tell all to the cops. Its only when Terry is acquitted in New Zealand that the Wilsons realise the potential consequences of their actions. What Terry doesnt know doesnt hurt him, but Terrys on his way back, hes got contacts everywhere and if he finds out the Wilsons dobbed, they're in deep trouble.

In episode seven of Underbelly, Terry decides to franchise his crime empire and expand into the UK market. Aussie Bob goes to extreme lengths to buy out Terry's share of the Organisation.

Allison questions her role in the Mr Asia syndicate after her life is threatened by a corrupt Federal Narcotics Bureau agent. Colourful racing identity, George Freeman, takes extreme action after police raid his illegal casinos. The Mr Asia syndicate suffers a major setback when a drug courier is arrested.

Aussie Bob Trimbole is pressured to arrange a gangland hit on his friend and colleague, Allison Dine. Meanwhile, paranoid and living in exile in the UK, Terry Clark must terminate his relationship with "Mr Asia". Also, George Freeman is determined to get revenge on his would be assassin, and aspiring hitman "Mr Rent-a-kill" gets his big break.

Terry Clark's drug empire starts to unravel when he is arrested for murder in the UK, while Allison is arrested by the FBI and becomes a star witness against organised crime. With his heroin supplies drying up, Aussie Bob plans Australia's biggest ever cannabis smuggling operation. Meanwhile, the Federal Police have a major win against corruption at the Narcotics Bureau.

The Federal Police prepare to arrest crime boss and cancer sufferer Aussie Bob Trimbole. But a mole within the Feds threatens to create havoc with their investigation. Also, Alison Dine testifies at a coroner's inquest, and blows the lid on the Mr Asia syndicate.

Australia's most dangerous hitman, Chris "Mr Rent-a-Kill" Flannery, moves to Sydney to build his deadly reputation. Terry Clark's UK murder trial reaches a sensational climax, but can Allison testify against her former lover? Meanwhile, Aussie Bob gets involved in arms smuggling for the IRA.

In the series finale of Underbelly, Chris "Mr Rent-a-Kill" Flannery becomes a victim of his own success. But who would dare order a hit on Australia's most dangerous hit man?