First, read Harper Lee’s 1960 Pulitzer Prize-winning TO KILL A MOCKINGBIRD.

Next, watch Horton Foote’s 1962 Oscar-winning screen adaptation.

Even if you’ve already done both, do them again.

Only then will you fully appreciate what Aaron Sorkin has accomplished in his play TO KILL A MOCKINGBIRD.

Yes, HIS play.

I can say this without question, for before I set foot in the Shubert, I read all 296 of Lee’s pages and watched all 129 minutes of Foote’s adaptation. As a result, I estimate that about 40% of the dialogue is Sorkin’s alone – and nearly 100% of it is riveting.

What came to my mind was a famous quip George S. Kaufman once made while he was watching The Marx Brothers performing one of his shows. After he endured their many, many ad-libs, he said to the person next to him in mock-astonishment, “I think I just heard one of the original lines.”

That seems true of Sorkin’s adaptation, which doesn’t just cannibalize what his previous authors had written. Sorkin has occasionally replaced but more often has augmented what Lee and Foote had written.

All those adapting should take Sorkin as their inspiration. (Are you listening, NETWORK’S Lee Hall?) Don’t just take the original author’s lines and add stage directions. Consider what other characters in the book are thinking and doing. Imagine what might have happened in scenes that the novel’s author never included. Find a new metaphor, as Sorkin did by giving a second meaning to the famous courtroom exhortation “All rise!” Work with skill and taste, and you’ll come up with a script that will thrill audiences the way that Sorkin’s script is doing now.

To review: Lee had six-year old Jean Louise “Scout” Finch tell what was then happening – and what she was feeling — in Maycomb, Alabama from 1933 to 1935.

Foote had an adult but unseen Scout occasionally add a piece of nostalgic narration while we saw young Scout and everyone else in action.

Sorkin has expanded Foote’s idea. He’s made Scout, her brother Jem and their friend Dill into adults. Now the three are looking back on what had happened in their youth: Tom Robinson, a black laborer, was accused of raping Mayella Ewell, a young white teen. The truth is that she was trying to seduce him and was caught by her father who was so incensed that he beat her mercilessly. Mayella, to explain away her injuries, had to claim that she received them while fighting off Tom.

When Scout, Jem and Dill were kids, they bought the sheriff’s declaration that Bob Ewell later died after he’d fallen on his own knife. Now, with the wisdom that comes with aging, they’ve grown skeptical. Wasn’t it all too convenient that the man who was out to terrorize or even murder the Finch kids just happened to inadvertently kill himself? So the three will be reviewing the situation.

In both Lee and Foote, Judge Taylor saunters by the Finch home and asks Scout and Jem’s lawyer-father Atticus to take Tom’s case. Sorkin doesn’t have the judge speak first, but instead has Atticus freely dispense his beliefs and opinions that Tom is innocent. After that passionate oration, how can he not take the case when asked? Sorkin shows us how Atticus’ passionate fairmindedness has painted him into a corner – a mighty black one.

Neither Lee nor Foote gave us Atticus’ first meeting with Tom in jail, where Sorkin mentions that the accused has been incarcerated for seven long months. Tom’s immediate concern is how this scandal has affected his children. As a result, Sorkin makes us see Tom first and foremost as a father. What parent in the audience won’t identify with his worrying about his kids and wanting to protect them from shame and scorn?

During this initial meeting Tom reveals that he “felt sorry” for Mayella, which is why he didn’t charge her for doing odd jobs. Those familiar with MOCKINGBIRD – and who isn’t? — know that Tom’s stating this on the stand is how he ruined his chances of acquittal. A black feeling sorry for a white woman was unheard of and inexcusable in ‘30s Alabama. Why would anyone so “inferior” sympathize with someone so obviously and automatically “superior”?

To our surprise, Atticus doesn’t tell Tom that saying that would be suicide; instead, he agrees to it – but only for a couple of seconds. He then realizes the perils of this stance, and gives Tom another option.

By taking this approach, Sorkin has allowed us to see another facet of the lawyer’s character: Atticus didn’t immediately realize the damaging implications of having Tom pity Mayella because he doesn’t think the way most others in town do.

The expected 12 chairs in the jury box are in place, but no jurors occupy them. Whether leaving them empty was Sorkin’s decision or exemplary director Bartlett Sher’s – or simply a budget consideration — the absence makes a shrewd observation and comment: Alabama in the ‘30s would automatically find Tom guilty even if Atticus proved beyond any sane person’s reasonable doubt that the poor soul were innocent. A black accused by a white in this part of the world back then might as well have no jurors, for few if any could be found with open minds. And to up the ante, Sorkin also establishes that prosecutor Horace Gilmer has never lost a case.

Did Sher or costume designer Ann Roth see to it that Bob and Mayella would wear their Sunday clothes for their courtroom appearance and be mighty uncomfortable in them? Mayella’s stockings are bunched up from her knees to her ankles; Bob has the wrong button buttoned on his jacket. A theatergoer could be pardoned for missing the latter, because Bob isn’t in court for very long. In another Sorkin masterstroke, when Atticus puts increasing pressure on Mayella, her father, who never had much cool to begin with, gets so hot under the collar that he lunges for Atticus. Judge Taylor then expels Bob from the courtroom for the remainder of the trial.

Imagine what the exiled Bob is feeling. He must be wondering what his daughter might say under even more pressure from sharp and experienced Atticus. For Bob, not knowing what’s going on is much harder than sitting in the courtroom, where he could at least hear and plan rebuttals.

Be prepare to gasp when Sorkin has Mayella state that whites are better than blacks: Erin Wilhelmi, who plays her, says the outrageous statement the utmost certainty and confidence. Whatever else Mayella may testify in court, this is one instance where she fully believes that she is indeed telling the truth and nothing but the truth. She, along with most everyone else in town, uses that N-word constantly, casually and without a shred of apology or awareness.

Foote added a vital component to Lee’s novel when he ensured that Tom was innocent because of a childhood accident. Sorkin improves on that by having townsperson Link Deas tell us in gory detail exactly what had happened to Tom. True, the best playwrights show instead of merely tell, but here getting the information makes us feel all the more for Tom.

When Tom is actually on the stand, what he chooses to say may be another surprise. Sorkin lets us see why he did it — and why he had to. The playwright also adds considerable dialogue to the famous post-trial scene where Bob comes to the Finch house to confront Atticus.

Many have criticized the scene in which Calpurnia, the Finch’s black nanny/maid, makes a frank outburst to her white employer. But Calpurnia has been in the Finch house for so long, taking the place of the children’s long-deceased mother, that she’s become a de facto wife to Atticus. Considering what’s happened to one of her people, Calpurnia might well have seen this as the straw that breaks her reticence and forces her to express herself in so forthright a manner.

She will now gain strength from Tom’s courage and will accept no excuses. For that matter, Atticus – who respects all she’s done for him — might well want to hear what’s on her mind.

In the end, Sorkin even provides a more graphic description of Tom’s fate. Like Lee and Foote, Sorkin sees that justice is served. It’s primitive justice and sure ain’t pretty, but it gets the job done. When dealing with a story about ’30s Alabama, we’ll have to take what we can get. And finally, Sorkin is able to make us feel more for the evasive Boo Radley than we’ve ever felt before.

As Atticus, Jeff Daniels, who became a household name partly in thanks to two silly films, shows in the courtroom scenes that he’s still dealing with Dumb and Dumber. Just as Sorkin has made the play his own, Daniels borrows nothing from Gregory Peck’s Oscar-winning performance. To be sure he has Sorkin’s new approach to thank, but this is a stronger and less remote Atticus.

As Tom, Gbenga Akinnagbe never loses his dignity, which is more than we can say for Frederick Weller’s effectively Neanderthalish Bob Ewell. But the real wonder is Celia Keenan-Bolger. With her Tammy Grimes nose centered under her bowl haircut, she’s no less than magnificent as Scout. Her range goes from astonishment as events unfold all the way to fury. She also gets in a hilarious moment when she uses her hand on the porch to show her frustration.

When the play resumed after intermission and she entered, I almost started second-act entrance applause. As the weeks go on, she’ll get it from others. After she moves on to her next project – or perhaps even for this one — she’ll get FIRST-act entrance applause.

Among the many smart decisions that Sorkin and/or Sher have made is not to have Keenan-Bolger’s Scout or Will Pullen’s (excellent) Jem and Gideon Glick’s (equally excellent) Dill raise their voices in silly falsettos, over-enunciate, open their eyes abnormally wide or pretend to be the children that Lee created. Even when the play goes back in time, they all speak in their normal voices and yet somehow make the audience forget that they’re not kids.

TO KILL A MOCKINGBIRD is a story of injustice; now one has been dealt to Aaron Sorkin. He’s had to endure seeing his effort called HARPER LEE’S TO KILL A MOCKINGBIRD on the side of the Shubert and in every Playbill.

No – this is AARON SORKIN’S TO KILL A MOCKINGBIRD and we’re lucky to have it. Here’s hoping the wrong against the playwright will be righted when awards season arrives.