It began with a lethal formula of black comedy and revenge-killing procedural, but bad twists and incest put Dexter on death row. It had a good run: from its debut in 2006, Showtime’s adaptation of Jeff Lindsay’s Dexter novels expertly marshalled its own absurdities to deliver a confident, darkly funny show like nothing around at the time. It was television’s first serial-killer procedural: a monster of the week format where Dexter assessed, tracked and killed whichever rapist, spree killer or assassin was in his sights. Rooting for the villain was nothing new, of course, but this took fanboying the bad boy to the next level.

Working as a blood-spatter analyst for Miami-Dade police offered Dexter the intel and expertise to carry out his campaign. He was the psychopath you could introduce to your parents. The show reached its peak with John Lithgow’s Trinity Killer of season four, a mesmerising big bad every bit as complex and formidable as our hero.

It couldn’t last. The wheels came off the juggernaut in season six. The villains were the Doomsday Killers, Professor James Gellar and his student Travis Marshall, who tried to bring forth the apocalypse with a string of Book of Revelation-themed killings. So far, so hoary. The story execution was even worse with the singularly non-threatening Colin Hanks scenery-chewing his way through a series of murder-scene tableaux.

“The killer is showing us a scene from the Book of Revelation,” Dexter’s co-worker Detective Mike Anderson helpfully pointed out as we viewed four dead horsemen: “Four horseman of the apocalypse. Doesn’t take a genius to figure it out.” Indeed, no, but the writers had a trick up their sleeves: a twist when Dexter discovers Professor Gellar’s frozen corpse in a freezer. The Gellar we’d been watching directing Marshall was a figment of Marshall’s imagination! The problem was that this curveball was telegraphed as early as the second episode, Gellar only interacting with Marshall and shooting off whenever another character appeared. “Painful and embarrassing,” said the AV Club of the reveal – and the fans agreed.

It was a brutal demonstration of the danger of twist-based storytelling in the internet age. With every episode pored over in forensic detail, you need to make your rug-pull disguise world-class. The false beard and glasses on the Gellar reveal fooled no one. The show tried to salvage a B-movie season premise with a straight-to-DVD twist. The clanking of chains from the TV cemetery grew ever louder.

Worse was to follow. Season six began the thread of Dexter’s adoptive sister Debra becoming sexually attracted to him. Incest dream scenes triggered viewers whose stomachs for mutilation and death were by now cast iron. The show pressed doggedly on for two more seasons, culminating in what is widely regarded as one of the worst series finales ever, with Dexter escaping justice by becoming a lumberjack. There was no last-minute reprieve for the show, however. It tangled with the Doomsday trope and saw its world end as a result. You could neither deny its glory days nor its flaws. Like a beautiful man who farts as he leaves the room, Dexter changed the world for the better, but left a noxious stink behind.