10 Best TV Show Twists You Never Saw Coming

10. Trinity Kills Rita - Dexter

It's generally accepted that Dexter began its brutal decline in quality following the season four finale, which ended with such a game-changing shocker of a twist that the writers seemingly struggled to know where to go next.

Season four saw serial killer-killer Dexter (Michael C. Hall) face off against the vicious, psychotic Arthur Mitchell aka the Trinity Killer (a brilliant, Emmy-winning John Lithgow), which culminated in Dex catching and killing him in the finale.

Dex then decides he's going to stop killing in order to truly settle down with his wife Rita (Julie Benz) and son Harrison, but upon returning home, discovers that Arthur murdered Rita before Dex caught him, leaving her bloodied corpse in the bathtub.

Worse still, Harrison is sitting in the bathroom in a pool of his mother's blood, just as Dexter did with his own mother as a child.

As twists go, this was as poetic as it was shocking, completely upending the series' formula in a totally fascinating and unexpected way, even if it also inadvertently signalled the series' downfall. Until it sort-of rebounded with the recent Dexter: New Blood, at least.