The invitation came last year, after Prast appeared in the irreverent musical comedy Rupert, about media baron Rupert Murdoch, and played - among others - former The Times editor Harold Evans. It was a small part, but Prast played the old-school style crusading journalist with such conviction McColl knew he'd found a "man of good moral fibre" to play Finch.
Smiling wryly Prast, who's had, at times, a lively past, says at least his law degree might finally come in handy. Given that he started ATC back in 1992, building it up and out of the defunct Mercury Theatre, and once ran for the Auckland mayoralty, one could suggest he's made use of that law school education many times.
Using Christopher Sergel's stage adaption, McColl says ATC's production will be utterly unflinching in its depiction of the events which unfold in a small town in the US's Deep South when a black man, Tom Robinson, is falsely accused of raping a white woman. Local lawyer Finch seeks the truth in a lone struggle for justice that inspires his children, Scout and Jem, and pricks the conscience of a community steeped in hatred and hypocrisy.
"Atticus Finch brings out the best that we can be," says Prast.
Perhaps because it focuses on the world as seen by 6-year-old Scout, Prast mistakenly thought To Kill A Mockingbird was a children's book.
"But, of course, it's not. It's most certainly a book children could and should read - along with any adults who have not - because of what it deals with: the oppression, racism, injustice and it has such a raw and visceral element to it.
"It's amazing that it's written through a child's eyes, with Atticus, as a father, doing his best to preserve and protect and hold the world together [for his two children] but the outside is there, creeping in at the periphery. Now that we're performing it at the Civic, I think audiences will get a very strong sense of the family being on an 'island of civility' surrounded by huge and dark forces."
He allowed himself one viewing of the film: "The last thing you want to do when you are playing a role as iconic and famous as this one is to bore anyone with your worst Gregory Peck impersonation."
Listen to set designer Andrew Foster and it becomes clear this version of To Kill A Mockingbird is liable to be unlike any other. Cedarwood poles will swing from the ceiling giving the production a dark and ominous vibe, says Foster who spent much time looking at 1930s photos of the US Deep South.
"You trawl through these photos and it very quickly goes from the idyllic to abject poverty with characters who are as weathered as the buildings," he says.
Asked about his preparation to portray Tom Robinson, actor James Maeva acknowledges the tragic and terrible truth.
"I didn't - I don't - have to look hard to see - to find out - what I need to know about these situations. We can just flick on any sort of device and see what's going on," he says, referring to the deaths of African Americans killed by police and the subsequent protests that highlight continuing racial inequalities in the US.
For his part, Prast says it's perplexing the same country that produced a story like To Kill A Mockingbird can also produce the type of divisive political campaign run by Republican presidential candidate Donald Trump.
"It's hard to see how such a country does not seem to be able to learn from its own lessons."
To Kill A Mockingbird also stars NZ film and theatre legend Ian Mune, Kevin Keys, Fasitua Amosa, Goretti Chadwick and a rotating cast of nine children, from ATC's academy for young actors.
Theatre
What: To Kill A Mockingbird
Where and when: Civic Theatre, May 5-28.
