The Leftovers delivered a truly insane episode this week, but beyond the bizarre and ambitious nature of it all was a character-driven story that culminated in heartbreaking fashion.

When the dead Kevin (Justin Theroux) found himself in a purgatory-like alternate reality, he learned more about his nemesis Patti (Ann Dowd) than he could have imagined.

Patti opened up about her tragic life in their final conversation in the well, before Kevin is forced to drown her and put an end to everything.

"When I got the script for [episode] eight, I was just floored," he told The Hollywood Reporter. "To me, it was such a bold move to just go there. Literally and figuratively, to go into that hotel - or into some form of purgatory - and revisit all these old characters that died in the first season.

"Then when I read the Patti arc, I was gutted because, for all intents and purposes, it looks like she does die. I was weeping at the end of it.

"The speech that she gives about Jeopardy, I thought it was one of the most beautiful [things]. It was where I really saw Damon [Lindelof] at the height of his powers.

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"I think he must have had lightning bolts shooting out of his fingertips at his keyboard when he wrote that scene, because I just couldn't believe how satisfying an arc that relationship took and how artfully he explained several things - Patti's intentions, Patti's use of silence, Patti's damage, Patti's literal inner child made real. He completely humanised her, in a way."

Theroux added that he found it difficult to film the scene where his character pushes a young Patti (Darby Camp) down the well.

"She's the purest form of Patti, which is what we all are when we're young - our purest selves, the most ourselves," he explained. "So Kevin's getting to see her as opposed to this screaming, smoking, white-wearing woman. He's seeing her true self, which is just a beautiful thing.

"I think it dawned on him that he has to move her forward. And the only way to do it was by killing her, to advance her through some sort of spiritual plane.

"It's interesting, because you could easily fade to black after he pushes her into the well, but then you hear that agonising, 'Kevin, help'. It just kills you. It killed me."

The Leftovers airs on HBO in the US and on Sky Atlantic in the UK.