Reese Witherspoon is in the national treasure stage of her career. There are other actors with greater range, and even more whose performances feel, well, naturalistic, but what Reese does is singular—signature, even—and enduringly, irrepressibly wonderful. It has just been over a decade since we’ve seen her at her Reesiest.

At last, in Big Little Lies’ Madeline Martha Mackenzie (a Reese character name if we've ever seen one), we have peak Reese, in all of her aggro-neurotic blonde glory. Nicole Kidman may give the most heart-wrenching performance in the show, but Reese's Madeline is the show's heartbeat. And nothing dictates tone and tempo like when Madeline stomps into a room, already mid-harangue.

To truly feel the amazing in Reese's work on Big Little Lies, we have to of course call out Tracy Flick, Elle Woods, and even Melanie Smooter, her fashion designer from Sweet Home Alabama (in that movie, she was on the cover of, yes, W). These are three shades of the same Reese archetype: success-obsessed overachievers who appreciate deviations to their immaculate plans about as much as they appreciate hold-ups in the Otter Bay Elementary pick-up line. Or yellow tape. Or Sade.

Is that Adele?

In the 15 years since Legally Blonde, Reese has proved herself an excellent dramatic actress—as June Carter in Walk the Line, as Cheryl Strayed in Wild—without ever really giving us the full Reese until Madeline, the tightly-wound, meddlesome mother in Big Little Lies. Like the most beloved of Reese's characters, Madeline is a little out of touch with reality, which lets Reese really flex her physical and facial comedic genius, whether it's in the service of destroying a child’s birthday party, or literally vomiting in her daughter's stepmother's lap (and front, and face). The more time you spend with her (Big Little Lies is, of course, Reese's prestige foray into TV), the more you realize that at the heart of Madeline's charm is a contradiction: She is both neurotic and lacks self-awareness. You can laugh with her, and you can laugh at her. This is the essence of Reese's appeal as a performer.

When Madeline learns that her daughter is going to live with her ex-husband, she says to her new husband, "She wouldn't leave if she knew I had cancer." "But you don't have cancer," Ed replies. "I'd be willing to get it," she says.

Big Little Lies would be so much more depressing without her.

But what good is a perfectly varnished veneer if it doesn't crack? Vulnerability, and the ability to flip the switch from comedy to melancholy with no lag time, is what makes Reese's the most compelling performance on this show, and what has sustained her performances over her career. In the penultimate episode, Madeline and Ed are discussing their sex life, or lack thereof—a subject on which Madeline likes to treat Ed as a dumb puppy who needs to brushed off all the time. But then Ed delivers the devastating line: “That’s the secret behind every happy marriage, the ability to pretend.” Madeline's face falls, her lip quivers, she leaves the room without stopping to get the last word.

I have nothing but praise for Nicole Kidman’s portrayal of Celeste—she wields her character's beauty like a sharp edge. Laura Dern even comes close to matching Reese for command of a room. But what you get from Reese is exactly what you want from Madeline: never cede a point (except when it makes you look better to do so), and never willingly lose a scene. Putting Nicole Kidman, Laura Dern, and Shailene Woodley around her only ups Reese's game. If you had to pick one person who is truly irreplaceable in this show, it has to be Madeline. There is no Big Little Lies without her. Let's hope she survives Sunday's finale.

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Watch Big Little Lies stars Reese Witherspoon, Nicole Kidman, and Shailene Woodley's screen tests: