The Shadow Line: When shots in the dark are right on target

To Victoria Park in Hackney to watch two men chasing a third – or to look at it from a different perspective, three men running behind a buggy on which is mounted a film camera. The lead actor – the one being hotly pursued across east London – is Tobi Bakare from the National Theatre, who is playing a driver whose passenger, an imprisoned drugs baron mysteriously granted a royal pardon, has just been shot dead. Bakare is being harried by Rafe Spall, who plays the dead drug baron's psychopathic nephew, who is in turn chased by Chiwetel Ejiofor as an amnesiac police detective. Confused? Well, it took Hugo Blick, who wrote, produced and is directing BBC2's distinctive new conspiracy thriller The Shadow Line, four months to work out what's happening in front of his cameras.

"The joys of conspiracy thrillers is that you had better know where you're going," he tells me between takes. "You can't write them à la Jeffery Archer and wonder how you're going to get to the end. I ended up on a white board in my room with a diagram looking like a double helix – and that's not the story that you'll watch, just what created the murder that the story begins with."

Blick is better known for his intimate and exquisitely observed comic monologues, Marion & Geoff (with Rob Brydon as the naively cuckolded taxi driver Keith Barret. Blick co-authored the 16 episodes with Brydon and directed them) and Sensitive Skin, the story of another disintegrating marriage, this time recounted by Joanna Lumley. He's certainly not known for epic seven-hour thrillers with a starry cast of over 70 actors, including Christopher Eccleston, Antony Sher and Stephen Rea as well the aforementioned Ejiofor and Spall.

"Marion & Geoff was an epic – it just happened to take place in a car," he counters, commanding the puffing actors back to their starting blocks for a fresh take. "But I dare say this is an opportunity for me to take my gloves off and start killing people."

The Shadow Line begins statically, with a hypnotically slow six-minute sequence in which two police officers, one of them obviously a bad 'un, pick over the corpse of Harvey Wratten, the recently assassinated drugs baron – the one who'd received the royal pardon. On the hunt for his uncle's killer is Wratten's nephew, Jay (Spall), a vicious, baby-faced and thoroughly unstable thug whose position in the gang has been usurped by his uncle's lieutenant, Bede (Eccleston). Sitting on the sidelines is the mysterious Gatehouse (Rea), while Ejiofor plays the investigating detective, Jonah Gabriel, riddled with self-doubt after a bout of gunshot-inspired amnesia.

The Shadow Line is not a whodunit, but a conspiracy thriller – albeit a very stylised one – the genre suddenly enjoying something of a renaissance. BBC4 is busy screening the American series Rubicon, with its tale of an intelligence analyst who uncovers a secret society of war profiteers manipulating world events, while currently filming in Belfast is Ronan Bennett's Undisclosed, starring Philip Glenister as a solicitor investigating his brother's death who uncovers, according to the BBC blurb, "a conspiracy that reaches deep into the heart of the political system".

Blick says: "Traditionally, conspiracy was always macro – big – they were oil, government killings, or in the Edge of Darkness – nuclear waste. "I was more intrigued in discovering something that absolutely matters to you and me. I can guarantee that within the last 10 days, if not the last 10 hours, you have worried about this thing. It's a universal fear that we all hold, but it's a personal one."

Sounds intriguing. Don't hold out for a second series of The Shadow Line however – not with this cast anyway. "I don't see it coming back – mostly because there's no one to come back to," Blick laughs. "Let's put it this way – the people who you think might live don't, and the people you think might die, don't."

'The Shadow Line' starts on Thursday at 9pm on BBC2