Louis CK’s experimental-ish Horace and Pete ended its season—maybe the whole series?—after ten episodes. It’s been an incredible run, and alongside American Crime Story: The People vs. O.J. Simpson, has been the best thing on TV this year so far, although Horace and Pete isn’t technically on TV. (They’re very different shows, so I don’t want to pick one or the other, but I’ve enjoyed both immensely.) The final four episodes are strong, but the finale is extraordinary. In the buildup we learn that Sylvie will get better, and that Pete will get worse, as her chemo is working, but his medication is being discontinued, forcing Pete back into an institution. When Pete, despairing, disappears, no one but Horace is really surprised.

For a show that felt thrown together more often than not, the finale episode ties the whole thing together in a calculated way that speaks to CK’s care as a writer. We go back in time, to the 1970s, and see Horace, Pete, and Sylvie as children, living with their abusive father, Horace VII, and their terrorized mother, Marianne. In a in interesting touch of continuity, CK plays Horace VII, Edie Falco plays Marianne, and Steve Buscemi plays Uncle Pete, Alan Alda’s character. Even Steven Wright pops in as a seventies-era barfly, which should feel like community theater, but instead works to establish that all this has happened before, and that Sylvie’s monologue railing against tradition was dead on—the bar and their family is a nightmare of abuse, repeating endlessly.

The acting is next-level throughout, but especially CK hits a career high as an actor playing the frightening and cruel Horace VII. The worst of the abuse is off screen, but the way VII physically dominates his wife is gut-wrenching, and his children obviously fear him, even as young Sylvie tries to stand up to him, she can’t run away fast enough. But the worst is young Pete (Nolan Lyons, Boardwalk Empire), a bright, energetic kid, but already showing signs of the mental illness that will devastate the rest of his life. We see the horrible moment that Marianne abandons Pete to VII’s brutality in order to save her children, and then after an intermission, the episode resumes in the present.

Pete is still missing, but Sylvie’s prepared to move out and “go see the country, or something” with her new man (Reg E. Cathey, wonderful as always). She encourages Horace to do something, to not just waste away in the bar, but then the police come to tell them they believe Pete is dead. Horace breaks down, and this is where the episode becomes extraordinary—Amy Sedaris shows up.

According to CK, Sedaris improvised her whole scene, and she transforms the finale. As Mara, a prospective waitress for the bar, Sedaris blows in at Horace’s lowest moment, an exuberant, friendly, hugger who talks non-stop and charms Horace despite his grief. Indeed, there’s a moment where Horace smiles at Mara that is half Horace’s own amazement at her audacious kindness, and half CK’s honest delight with Sedaris. Professional admiration bleeds through and yet instead of breaking the flow, it adds to it, and you can see in that moment, Horace falls in love. And the show could have ended right there. Mara comes in and changes Horace’s life, he decides what he’s “going to do”, fade to black, and we end with the cycle of Horace and Pete’s broken.

But that’s not the lesson taught in the first half of the episode. The point of the first half, driven home by the recycled casting, is that nothing changes at Horace and Pete’s, and escape comes with a cost. Marianne escaped at the expense of young Pete, and Sylvie, with her plans to leave Brooklyn, will have to pay her tithe, too, and it’s terrible. But Horace and Pete is pretty bleak, and the ending is as emotionally harrowing as anything on the show. And it’s fitting it ends on Sylvie, as the series has been a showcase for startling, amazing performances from women. If you watch no other episode of Horace and Pete—though you really ought to watch the whole thing—watch the finale. It works as a stand-alone, and it REALLY deserves to be seen.

You can purchase episodes of Horace and Pete here.