Quick Answer: The Fall immediately introduces viewers to the murderer, Paul Spector, thus moving away from the typical "whodunnit" format. But without a mystery for the audience to solve, what makes The Fall so suspenseful and compelling to watch? Part of it has to do with Spector's character, whose double life keeps viewers engaged and on their toes. Also crucial to the show's mounting suspense is the continual game of cat-and-mouse between Spector and DSI Gibson. Finally, the show employs a fickle hand of fate that constantly turns the tables on both sides of the law.

For many crime dramas and psychological thrillers, the degree to which they are successful depends on their ability to build suspense. As such, it's common for these dramas to keep audiences in the dark, only revealing the killer at the very end. The BBC's The Fall (2013 - ) flips this format on its head, immediately introducing viewers to the murderer, Paul Spector (Jamie Dornan). Inverting such a tried-and-true crime-solving format begs the question: without a mystery for viewers to solve, what makes The Fall so suspenseful and compelling to watch?

Paul Spector (Jamie Dornan) with his family

Part of the answer is Spector's duplicitous character. Spector is a man leading two lives at once. On one hand he's a husband, a loving father, the man who helps Liz Tyler escape from her abusive husband; on the other he's a stalker, a serial killer, the man who photographs his victims after rearranging their bodies into poses. Dornan has stated that he plays Spector as two distinct characters, almost as if Spector has split personalities. Part of the show's charm, then, is the glimpse it offers at a family man who is also a murderer. Here, the audience gets to witness this complex duplicity first hand. As the show progresses it becomes more and more difficult for Spector to keep his two lives separate, which only makes his character more fascinating. As the two lives slowly meld into each other, even Spector himself has difficulty reconciling his love for his daughter and his abuse of women. 

Karen Hassan as Annie Brawley and Jamie Dornan as Paul Spector

As we can see, The Fall isn't so much a "whodunnit" as it is a "whydunnit," and the theme of duality is central to figuring out Spector's motivations. Detective Superintendent Stella Gibson (Gillian Anderson) is quick to point out this theme. She also recognizes that the villain isn't the only character who exhibits some sort of twoness. As she tells pathologist Reed Smith (Archie Panjabi), "There's a name for it. It's called doubling. I do the same. So does the killer." And it’s true – Gibson shares this trait (among others) with Spector. In fact, the criminal and the detective are so closely mirrored at times that they almost seem to be doppelgängers. 

Like Spector, Gibson is key to the show's captivating effect on viewers. It's the interplay between these characters on both sides of the law that keeps audiences hooked. Indeed, the deadly cat-and-mouse chase is the thrust of the series. Gibson makes a move to capture Spector, who makes a move to kill again, accentuating the chess-like feel to the show. Watching The Fall, then, has the feel of watching a high-stakes sporting event between two well-matched opponents. 

Jamie Dornan as Spector and Gillian Anderson as Gibson

The other main source of suspense comes from everyday circumstances that affect the characters. The show organizes itself around weird twists of fate that, though seemingly innocuous, can lead to a criminal's downfall. Such was the case for a number of real-life criminals. David Berkowitz, a.k.a. The Son of Sam, was only caught because of a parking ticket he received at the scene of one of his murders. Timothy McVeigh, the Oklahoma City bomber, was caught during a routine traffic stop for driving without a license plate. Ted Bundy was similarly caught for driving infractions.

The same types of coincidences add layers of suspense to The Fall. For example, when Spector is caught scoping out his next victim's house, he pretends he's on his way to meet Liz Tyler (Séainín Brennan). This leads her husband Jimmy (Brian Milligan) to believe that they're having an affair. Spector later evades the police in the gardens, only to run into Jimmy on the street. The encounter causes an altercation, leading the police directly to Spector. Chance has a similar effect on the police, causing investigations to not go as smoothly as planned. During the bugging of the Spector house, for example, one of the officers falls through the ceiling, ruining the operation. 

Jamie Dornan as Spector and Colin Morgan as Detective Sergeant Tom Anderson

Though Spector and Gibson's game of cat-and-mouse certainly creates the lion's share of The Fall's suspense, the show's numerous twists of fate are unique in that they don't adhere to any moral code. Both the good guys and the bad guys alike are affected by coincidences and sharp vicissitudes. As a result, the show makes viewers constantly question what will happen next: will Spector be found hiding in Gibson’s hotel room, or will he murder her in her sleep? Will Spector escape, or will he be killed in the street by a jealous husband, or will the police capture him? The Fall proves that though we may have known the killer's identity from day one, there is certainly no shortage of questions to keep viewers on the edge of their seats.