That was truly, truly disturbing.

It doesn’t always happen, but at least once a season “Game of Thrones” delivers an amazing episode of television. Sunday’s “The Rains of Castamere” was such a moment.

For about 15 minutes, the show’s writers, actors and directors transformed HBO into a bloody, unsettling horror movie.

At the wedding reception for Edmure Tully and Roslin Frey – an arranged marriage designed to unite houses in a war against the Lannisters – Walder Frey committed a massacre, slaughtering Robb and Catelyn Stark.

Fans of the books know this moment as the “Red Wedding,” but the scene in the books is so ghastly I wondered if it could be properly recreated on television. The show changed the scene (in the books, the music is more horrible; the party is more drunken; and there’s this great swirling feeling to the chaos) but didn’t lose an iota of its horror.

And the slaughter of Lady Talisa along with her and Robb’s unborn child (though not in the books) took the massacre’s cruelty to an even greater height.

I knew it was coming, and it still really unsettled me.  Bravo, Messrs. Benioff and Weiss. Bravo.

To recap: Robb had been planning an attack on Casterly Rock (to strike the Lannisters in their home) but he needed armies pledged to Walder Frey to achieve that.

Edmure, Catelyn’s brother, agreed to marry Roslin Frey (who, luckily for Edmure, was far from ugly like the rest of the Frey girls) in an attempt to unite the houses.

At The Twins (Frey’s castles), Robb even begged forgiveness from the multiple Frey daughters for breaking his vow to marry one of them, and choosing Talisa instead.

“All men should keep their word. Kings most of all,” he said

Lord Walder Frey pretended to understand and accept Robb’s apology. Frey gave Robb, his family and his men food and drink (the customary promise of protection) inside his home. Aside from his typically creepy comments about women (including Talisa whom he referred to as “firm tits”) Frey appeared to be agreeing to join forces with the Starks.

“The wine will flow red, and the music will play loud and we’ll put this mess behind us,” he said.

But at the wedding reception, Catelyn suddenly noticed that something was amiss.

The revenge song “The Rains of Castamere” began to play in the reception hall, and a solider locked the doors shut. Outside, Robb’s wolf Grey Wind also sensed danger.

Catelyn reached for Roose Bolton’s arm, and realized he was wearing armor under his wedding attire.

Then Walder Frey, calling it a “wedding gift,” gave the order to attack. Archers rained down arrows from above, and a solider ran up to Lady Talisa from behind, stabbing her and her child in the womb multiple times.

The Starks were ambushed, caught unaware, without protection and outnumbered. The massacre was ferocious and animalistic.

Robb and Catelyn were struck with arrows, and a badly injured Robb crawled across the floor to lay with his dying wife.

Catelyn, desperate, grabbed Walder Frey’s wife, and held a knife to her throat. Catelyn begged for Robb’s life and threatened to kill her if Frey didn’t agree.