Commissioner Metcalfe is relishing the financial returns of selling off a disused training facility to Tredmon Holdings, a private company. Bill questions the merits of selling off valuable assets, but Metcalfe isn’t interested he’ll be long gone before any fallout. Bill has devised a plan to deliver the budget savings demanded when he took the job but without cutting a single copper. Cycling at night, Bill spots a bonfire blazing in a field: a pyre of blackened bodies. Five victims, male; each with a nail embedded in the back of their skulls. Until now, there have been seven nail-gun killings in nine years in the UK, all traced to one man: Frank McGill, convicted and sentenced in 1997. An older man now at 71, McGill’s whereabouts are unknown he has disappeared. McGill was once a favoured hitman of the Macguire gang, many of whom were convicted on the evidence of an informant around the time of his conviction. Could he have gone into witness protection?

The Protected Persons Service refuses to divulge anything. Bill is in trouble over the Boston Bandit case. DS Blair’s lawyers claim police misconduct due to DNA evidence unlawfully obtained. He is released on bail. The scandal is splashed over the front page of the Boston Stump, with Bill as the fall guy. With Metcalfe manoeuvring to oust him, Bill considers his options: maybe it’s best he and Kelsey move on. Further examination indicates the victims were frozen before being burned. Bill identifies a property sold to the National Crime Intelligence Service in 1997. His team finds the house deserted, uninhabited for over a decade, except for a skeletal corpse discovered in its walls. McGill went missing from Witness Protection in 2008, after a visit from a Maguire associate (the body in the wall), come to exact revenge.

At home one night, Bill is wracking his brains to find this man when a nail-gun is poked into the back of his head: Frank McGill has found him. McGill denies the murdering the five men. As Kelsey comes downstairs, McGill disappears, unseen. A muddy footprint his sole trace. The pathologist finds the five recent victims were dead before the nails entered their skulls. She theorises that these men were homeless; unidentified, they would have been kept in deep freeze. Someone stole these bodies from the morgue and tried to frame McGill. Suspect number one: Terence Maguire Junior. McGill’s muddy footprint contains high salinity, characteristic of the mud at Freiston Salt Marsh.

Bill stakes out the marshes and discovers Frank’s house, hidden in the woods, and Frank himself armed with a shotgun. Bill has inadvertently led Terry Jr. straight to Frank’s door and now finds himself in the middle of a deadly vendetta. He slips away from the coming fire-fight, only to walk into the sights of DS Alec Blair. Frank fires first and Blair drops dead. A decades old blood-feud a story of love, lies, tragedy and murder ends in a climactic fire-fight, and the deaths of Terry Maguire Jr. and Frank McGill. Father and son. Maguire and Krasnov were working together to reap the profits of a corrupt merger of the two Lincs police forces, enabled by Metcalfe. Bill has Metcalfe over a barrel and twists his arm to press forward with a new merger in the public good, with Chief Constable Bill Hixon taking charge of Greater Lincolnshire.

The Final episode of Wild Bill airs 17th July 2019 on ITV at 9pm