Television takes risks. In the age of Peak TV, shows take you on a journey–and the best shows take you someplace you didn’t even know was on the map. People plot their lives around avoiding spoilers for shows like Game of Thrones, The Walking Dead, and Stranger Things. Surprises are such a part of TV that they no longer exist solely in the domain of drama; The Good Place is a high-concept comedy that begs you to remain clueless, lest you ruin the show’s constant surprises.

But this wasn’t always the case.

Sure, TV has always been a surprising medium, and plot twists like “Who shot J.R.?” kept viewers on their toes before I was even born. But even the most daring shows still had a status quo to uphold. The X-Files pushed TV forward by incorporating a long-running conspiracy plotline, but the show still settled back into Mulder and Scully’s monster-of-the-week groove in-between mind-blowing reveals. Shows had a rhythm, characters had their roles, and deviations were not expected.

And then viewers got a big surprise with an episode of Buffy the Vampire Slayer appropriately titled “Surprise.”

I don’t think it’s an overstatement to say that that episode, written by Buffy Hall-of-Famer Marti Noxon, and its companion piece “Innocence” (written and directed by series creator Joss Whedon) truly changed television when they first aired on back-to-back nights in late January, 1998. I remember what it felt like watching Buffy Season 2 as it aired, and how the season–really the entire series–was cleaved into halves by this two-parter.

I’m not going to get into a beat-by-beat recap of “Surprise” and “Innocence,” because they’re episodes you really should watch if you have 90 minutes free this weekend. Watching them is watching a show not only kick into high gear, but redefine what a TV show is allowed to do. Before “Surprise,” Buffy was a low-budget, beloved cult fave on an upstart network, one that balanced monster-of-the-week episodes with villain-of-the-season ones not unlike The X-Files. After “Innocence,” however, the scope of what the show could do was blown out. That’s because, and I will now give a spoiler warning for two 20-year-old episodes, the show turned its love interest into the season’s main villain–and didn’t back away from that decision.

By now I’m sure everyone knows that twist, so my spoiler warning was probably for nothing. But at the time, this was a major event made more major when Angel’s soul was not restored by the end of “Innocence.” Buffy’s main squeeze since the early days of the show, the tortured vampire with a soul played with swoonworthy broodiness by then-newcomer David Boreanaz, went from angel to devil with no warning and no quick fix. Angel was Buffy’s boyfriend! He was in the opening credits! Characters in the opening credits don’t turn evil!

The change came through the best use of Buffy’s tried and true monster-as-teenage-angst storytelling device. After a lot of kissing, fretting, love, discussion, and drama, Buffy loses her virginity to Angel, the vampire with a soul that she reckons is her soulmate. And then, the next day, he’s changed. He’s distant. He’s flippant. He’s mean. He got what he wanted and he walks out the door with a thrown off “I’ll call you.” What Buffy doesn’t yet know is that Angel was cursed with a soul, a curse that was only maintained so long as he was in emotional torment. A second of pure happiness and BAM, curse rendered pointless. After a night of pure happiness, Angel returned to being the marauding and sadistic Angelus, the vampire he used to be. This leaves Buffy, played with such vulnerability and resolve by Sarah Michelle Gellar, wrecked.

The metaphor is right there: Buffy has sex and the guy loses his soul in the morning, breaking her heart. In the world of Buffy, though, that metaphor becomes literal–and, in a true twist, it lasts. Angelus is not ensouled by the end of the two-parter, which was no doubt what viewers subconsciously expected to happen since that’s how TV worked at the time. Shows were cursed with maintaining a status quo, but Buffy broke the curse.

Angelus’ arrival gave the show a true equal for Buffy, and it gave focus to the chaotic but meandering antics of Spike (James Marsters) and Drusilla (Juliet Landau) as the big bad vamp took charge. The show felt more dangerous than ever, as Angelus was once welcome in the heroes’ homes (a real problem with vampires). Angelus remained evil for the back half of Season 2, his reign of terror stretching from “Innocence” (where he tries to kill a department store full of people using a Smurf-on-steroids demon) to “Becoming, Part 2” (where he tries to send Earth to literal Hell). So no, “Innocence” didn’t end how viewers expected it to end, with Buffy and Angel’s love strained but healing. It ends with Buffy kicking Angelus in the balls, vowing that she will kill him.

In pulling off this overhaul of the status quo, Buffy became the kind of show that viewers could not miss and it frequently delivered the goods. Slayers defected, eyes were gouged, heroes were shot, songs were sung, death always lurked around the corner from laughter–Buffy went from a quirky cult show to a weekly event. Pain even lingered on long after the deed was done, evidenced by the entire Scooby Gang’s reluctance to let a tortured (but soulful) Angel back into their ranks through Seasonout 3. Choices suddenly had intense, long-lasting ramifications on Buffy.

From there, television evolved. The Sopranos, an HBO drama with unflinching commitment to being unpredictable, ushered in the idea of “prestige TV” in 1999. J.J. Abrams’ spy drama Alias debuted in 2001 and packed in “Surprise”-level surprises every season. The Buffy writers themselves went on to Lost, Battlestar Galactica, Mad Men–shows known for being unpredictable. Whether or not some or all of those shows were inspired by Buffy, who really knows. What’s clear, though, is that Buffy pulled off one of the greatest status quo shakeups in TV history and did not back down from the ensuing challenge of being the kind of show that did things like that. “Surprise” and “Innocence” gave TV the kick in the balls it needed.

Watch Buffy the Vampire Slayer's "Surprise" on Hulu

Watch Buffy the Vampire Slayer's "Innocence" on Hulu