LONDON — It must be great fun having Robert Sean Leonard’s stage career. On the American stage, the co-star of the popular television show “House” has made playing Brits something of a habit, most notably in the plays of Shaw and Stoppard, winning a 2001 Tony for the latter’s “The Invention of Love” along the way.
At the same time, his chosen forays on to the London stage have been iconically American. Mr. Leonard, a New Jersey native appeared alongside Alan Alda in a West End revival of Thornton Wilder’s “Our Town” 22 years ago, and he has returned to the capital in an al fresco staging of Harper Lee’s “To Kill a Mockingbird” that — guess what? — has been directed as if the material to some degree were “Our Town.”

Wilder’s benchmark play was written just a few years after the events in Ms. Lee’s celebrated 1960 novel take place. Both works make of their separate and specific locales — rural New Hampshire in one instance, Depression-era Alabama in the other — a site of convergence for humankind in all its flawed and troubling diversity.

The difference, of course, is that Ms. Lee’s novel has had to be adapted for the theater, and on this occasion, it is a version by the late playwright Christopher Sergel. And whereas “Our Town” two decades ago seemed to mystify British commentators who couldn’t see beyond the apparent folksiness of Wilder’s fundamentally grievous script, “To Kill a Mockingbird” has long occupied pride of place in the English literary psyche: The book is studied by generations of schoolchildren here, just as it is across the Atlantic.

How, then, does Timothy Sheader, the director, begin the evening? By marking out his terrain with an implicit nod to “Our Town.” Before we have fully clocked them, the aisles of Regent’s Park’s Open Air Theatre are alive with various actors reading excerpts from dog-eared copies of Ms. Lee’s novel, while a sense of place comes from drawings made on the stage floor of Jon Bausor’s purposefully bare set. (The cast carry on and off the required props.)

The company functioning as a collective stage manager then clears away, and the story proper takes hold: The time-honored tale of 6-year-old Scout and her older brother, Jem, and their relationship with their widowed father, Mr. Leonard’s Atticus Finch, whose abilities as a lawyer are not necessarily matched by his parenting skills.

Few probably need reminding of the racial climate explored across an evening that finds Atticus defending a black man, Tom Robinson (Richie Campbell), against charges of rape, the second act given over to an extended courtroom scene that posits the show’s spectators as the ad hoc jury.

And before very long, one is aware that considerably more is at stake than simply this one man. What sort of society do we want to inhabit? That question hovers in the notably frigid (at the opening performance anyway) night air, the ending suggesting a healing of sorts on the domestic front that the world at large will choose to follow or not, as it sees fit.

It is possible for the events on view to devolve into a civics lesson in three dimensions, and there were moments in the first half when I began to wonder whether we were getting an actual dramatization of the novel or merely an annotation of it. (Something of the same issue besets the Olivier Award-winning “Curious Incident of the Dog in the Night-Time,” which itself relies on extensive narration to propel its way forward.)

But after the intermission, the innate power of the piece grips anew, so much so that one stops fretting about how a cast — the children, especially, seen wearing short-sleeved shirts and shorts — is managing to stay warm at the outdoor theater amid such unwelcome February weather in May. (Adrenalin, I suppose, with a bit of warmth presumably thrown off by the stage lights.)

It helps that this “Mockingbird” is yet another production to showcase London’s seemingly ceaseless abundance of child actors, which musicals like “Billy Elliot” and “Matilda” have done their bit to promote. Indeed, among the three young actresses alternating in the defining role of Scout is a onetime Matilda, Eleanor Worthington Cox. At the press performance, the role was taken by the newcomer Izzy Lee, who with this play makes her professional stage debut. We will hear more of her: Ms. Lee is as commendably firm-voiced as she is firm of purpose in her ability to draw an audience toward her.

Among the adults, the company gets to demonstrate a gift for accents as its members recite one or another passage from the novel in their own voice, shifting to the sounds of the American south once the play itself kicks in. Mr. Leonard, for his part, has the inevitably daunting task of dispelling — or at least putting to one side — our memory of Gregory Peck’s Oscar-winning turn as Atticus on screen.

That he entirely succeeds honors the unforced gravity and grace of this nattily attired man of principle, a rhetorician who comes alive in a court of law but elsewhere gives off the poignant feel of a man shadowed by loss. In truth, the actor may be a tad too youthful in appearance to communicate the “tell-tale creases” that the aging Atticus is said to possess, but the performance reaches out directly to what matters most — the awakening of the heart, notwithstanding the abrasions of the community at large.

As for his future, one can only envy audiences at the Williamstown Theatre Festival who will be able to see the role Mr. Leonard takes on next — Henry Higgins in “Pygmalion,” starting performances in the Massachusetts town on June 26. By rights, after his spending several months in London, that accent should be a piece of cake — or scones with clotted cream and jam.

Plays don’t come much more English than Alan Ayckbourn’s “Relatively Speaking,” at Wyndham’s Theatre in the first West End revival since its 1967 London premiere announced a subsequent mainstay of the London stage as a comic force to reckon with.

As ever with Mr. Ayckbourn, who has now written more plays (77) than he is years old (74), structure is all, and one can only marvel at the way in which he builds a simple misunderstanding involving two couples into a mirthful authorial gavotte flecked, as is the norm with this playwright, by hints of darkness just beyond its sunny climes.

Exposing more flesh than one assumes would have been the case 46 years ago, Max Bennett is suitably bemused as the still-new boyfriend to the pert and peppery Kara Tointon, whose efforts to bring to an end her affair with the far-older (and very married) Jonathan Coy send domesticity spiraling into disarray.

I haven’t always warmed to the show’s biggest name, Felicity Kendal, whose gurgling stage persona can be winsome to a fault. But as a wife who turns gradual enlightenment into what may just represent her character’s best chance of escape, Ms. Kendal’s perpetual good cheer takes its place among the funniest, and smartest, coping mechanisms of any play in town.

Harper's Lee novel, set in Alabama during a Depression when poverty and racism walk hand in hand, is one of the great stories about growing up. For many of us, the tale of Scout's journey from innocence to experience as her lawyer father defends a black man accused of raping a white woman is part of our growing up, too.

Timothy Sheader's canny staging recognizes the way this novel has been woven into the fabric of our lives, and constantly reminds us that books like Mockingbird, are something precious and shared – like theatre itself. In the opening moments, the performers pop up from within the audience, reading from dog-eared editions of the novel in their natural accents. Throughout, they share the narrative, helping to make a virtue of Christopher Sergel's authorised but now old-fashioned 1991 adaptation.

It's a lovely touch, and takes us straight back to childhood. So, too, does the roughly chalked, child's-eye map on the stage of the small town where the action is played out. It is a complete world for Scout, for her older brother, Jem, who is teetering on the brink of puberty, and for their odd friend Dill (apparently based on Truman Capote), who lives mostly in his own imagination. The children (Eleanor Worthington-Cox as Scout, Callum Henderson as Jem and Sebastian Clifford as Dill) are played beautifully without any sentimentality, and Robert Sean Leonard's Atticus hints at emotional damage lurking just beneath the closed, squared-jawed decency. It all sets the tone for a performance that is direct, simple and unshowy.

Even on the warmest days, Regent's Park is never going to be a convincing stand-in for the American deep south, but the rustling trees and lengthening shadows create exactly the right sinister atmosphere, and what the show lacks in physical heat it makes up for with heart. The amphitheatre provides a natural courtroom in the second half as the trial of Tom Robinson (Richie Campbell) unfolds and tensions in the town rise. Perhaps the final appearance of the reclusive Boo Radley draws a little too obviously on Edward Scissorhands, but if one measure of a stage adaptation's success is that it sends you scurrying back to read the original novel, then this production scores highly.

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