The Suspect director reveals how they filmed tense opening scene

Joe is safely strapped into a harness but drops a second harness intended for Malcolm – as a result, we learn, of early onset Parkinson's disease – and so initiates "plan B", removing his own safety equipment and giving it to Malcolm.

But as Joe is still securing the harness, Malcolm loses his footing, falling from the ledge and taking Joe with him. The two men end up dangling mid-air, Malcolm barely secured by a loosely-fastened harness and Joe holding on to him for dear life.

Eventually, both men are saved when the emergency services arrive, tossing Joe a line which he uses to pull himself and Malcolm back inside the hospital through an open window.

• Aidan Turner says filming tower block stunt in The Suspect was "terrifying"

Speaking to RadioTimes.com, The Suspect director James Strong revealed that plotting and shooting the tense sequence was "an incredibly complicated process".

"I've been fortunate enough to do a couple of those sorts of things – there was actually an episode of Doctor Who called Partners in Crime, where David [Tennant] and Catherine Tate are hanging out a window, so that was kind of reminiscent of this."

Detailing the work that went into planning The Suspect's opening, Strong explained: "Firstly, you've got to work out what shots you want, so you do storyboards or shot lists – a bit of both – and you kind of imagine a sequence in your head, and then you work out how to get each one of those shots...

"It then breaks down to what we could do at a real location – and then obviously working with the constraints of that location, and what the insurance will let you do, and what you can do with visual effects. So all those things are considerations – time, money, all that stuff."

First, stunt doubles were filmed on a ledge several floors up at a real London hospital, with drone shots capturing the footage as well as shots of fire engines and ambulances on the ground below. "You're trying to sell it as a director," Strong said. "VFX is so good these days, I probably didn't really need to have have people on a ledge. But psychologically I felt you would know, and you can tell.

"You could do it [with visual effects]. But I just think subconsciously, somewhere, you know."

These shots were then combined with close-up footage of actors Turner and Kongolo – filmed, Strong revealed, "in a car park in Dagenham".

But while the two performers might not have been out on a real hospital ledge, a section of the ledge was recreated for their portion of the shoot and was, according to Strong, "still quite high".

"All those elements are really important," he concluded. "If you miss one of them, it doesn't quite hang together. We actually went back later and shot some close-ups of the strap [when Joe and Malcolm are hanging and the harness threatens to come loose], which really sells it."

Read more:

• The Suspect's Aidan Turner casting 'plays with audience expectations'
• Aidan Turner thriller The Suspect almost got made 5 years ago
• Aidan Turner says meeting with Parkinson’s patient for ITV’s The Suspect was "invaluable"

The Suspect continues on Monday nights at 9pm on ITV, with episodes also available after broadcast on ITV Hub.

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