Harry Venn (Glenister) is a small-time solicitor who is forced to revisit his murky past and quickly finds himself caught up in a much more complex and deeper conspiracy.

Episode 1

Harry is approached by Gina Hawkes, a lawyer looking for a missing alibi witness for her client – the witness being an old acquaintance of his, the long-term criminal Joe Collins.

The case reminds Harry of his own brief criminal past as a getaway driver for his older brother; a venture that ended with the death of his brother and their associate Hillman in a robbery that went horribly wrong.

The guilt Harry feels from this incident drives him to uncover what went awry in a seemingly simple operation. His only lead is that he knows the killings were commissioned by a man named Styles.

Tom Russell, the policeman who led the investigation all those years ago, is back on Harry's case, and with the past swiftly unravelling at every turn, Harry begins to question exactly who Gina is and why she chose him.

Episode 2

With his office blown to pieces, Harry is determined to find out who Gina Hawkes is. He gets his friend and accomplice, Frank Hanna, to break into her doctor's office to access her files. But when Hanna is chased out by armed heavies he realises they are caught up in something far more dangerous than they originally thought.

With no new leads, Harry thinks Gina's barrister, Nigel Fountain QC, might be able to unlock the mystery. However, he is unforthcoming, leaving only the imprisoned Stevie Quirke to supply any clues. Harry goes to visit him but what he finds rattles him. In one last desperate bid, Harry tracks Gina to Paris, only to be confronted by a past he thought he had long since left behind.

Episode 3

In Paris, Harry and Gina are held at gunpoint by Hillman – only to find themselves saved by a masked gunman.

Tanzir has been mortally wounded, but Harry hears him say "Styles" with his final breath. Harry confronts Gina about why she's been lying up until now and discovers that her parents died 20 years ago, on the same night Mark was murdered. Could they be looking for the same person?

Back in London, Gina's visit to Sir Nigel Fountain is cut short when Styles appears at the door under a false name. She makes a quick escape, devastated by the implication that Nigel must somehow be involved. She goes to meet Harry and Frank and together they head to Kent to the house where it all started 20 years ago. Ben Lander still lives there – the only survivor of that fated night – and their visit does not quite go as planned.

Episode 4

In the aftermath of the shootout in Kent, Frank Hanna lies injured, as Ronan Bennett's four-part conspiracy thriller concludes. Unable to alert the police to what's happened, Harry and Gina drop him at a hospital and head to see Joe Collins in a hotel room near Heathrow.

Collins is in a desperate state. He tells them he was hired to do a job for Styles a while back but changed his mind. However, rather than walk away, he made the fatal mistake of stealing his laptop. Realising its contents probably hold the answers, Harry takes the laptop and heads to Lauren's with Gina. In the morning, the two of them split up: Gina goes to Nigel Fountain for answers, while Harry finds someone to break into the laptop.

Both trips deliver some unexpected truths, and Harry suddenly realises he has less than an hour to stop an event that could change everything – not just for himself but for the country. In a climactic showdown, he is forced to confront the past that has long haunted him.

Cast

Harry Venn is played by Philip Glenister, Gina Hawkes by Thekla Reuten, Elspeth Verney by Anna Chancellor, Mark Venn by Mark Powley, Paul Hillman by Mark Flitton, Fenton Russell by Thomas Craig, Dr Sturgess by Richard Durden, Frank Hanna by Richard Dormer, Jason Styles by Peter Guinness, Steve Quirke by Paul Ritter and Lauren by Lisa Kay.

Photograph shows Philip Glenister and Thekla Reuten in character as Harry Venn and Gina Hawkes

The DVD for this series will be available after the programme has aired.