Two London productions that play fast and loose with their literary sources lack the theatrical magic of another show that gives viewers the original, unadorned.LONDON — If you’re going to revisit a classic novel by a woman, you should probably give that task to women. That’s the conceit behind “Pride and Prejudice* (*sort of),” a play that’s now at the Criterion Theater here for an open-ended run. The production, a success at the Edinburgh Festival in 2018, will most likely appeal to those with no time to actually read Jane Austen: Let the five gifted performers of the all-female cast relay the novel in their own larky, irrepressible way.The parenthetical in the title sets the cheeky tone. Written by Isobel McArthur “after Jane Austen,” as the playbill puts it, the show gives us all the time-honored characters, from the self-dramatizing Mrs. Bennet to her five matrimonially challenged daughters. Nor are the men excluded: McArthur, the author, doing triple duty as the play’s co-director (with Simon Harvey) and as one of the hard-working cast, drops her voice as required to play Fitzwilliam Darcy, the book’s abiding heartthrob.Putting a contemporary spin on a Regency-era tale, the play co-opts music to make a point: Barely has the bride-to-be, Elizabeth Bennet (a gleaming-eyed Meghan Tyler), fallen under the sway of Mr. Darcy before she launches into the Carly Simon standard “You’re So Vain.” In the let’s-try-everything spirit of the venture, the cast members also play musical instruments, and there’s a reference to “The Phantom of the Opera,” which is playing around the corner, in an opening sight gag involving a falling chandelier.The intention is to play fast and loose with the source while honoring its spirit, which for the most part succeeds. Mr. Darcy’s eventual confession of his desire for Elizabeth is accompanied by the swelling sounds of the Partridge Family’s “I Think I Love You.” The overbearing Lady Catherine de Bourgh (Christina Gordon) enters to the music of the sound-alike Chris de Burgh, and we hear expletives that would surely have made Austen herself blush.The all-female cast brings a party vibe to Jane Austen’s iconic love story.Matt CrockettI wish more had been made of the suggestion at the outset that we will be viewing these characters from the perspective of the servants, whose employment enables the Bennets’s leisurely lives. At the beginning, the performer Hannah Jarrett-Scott galumphs about in Doc Martens, busy with her cleaning chores and not quite ready for the show to begin. (“We haven’t started yet,” she exclaims.)But any sort of class commentary soon disappears. This is “Pride and Prejudice” with a party vibe. “Are you having a good time?” we’re asked late on, to which the audience members at a recent matinee responded at the curtain call by leaping to their feet.Playfulness with a resilient source also informs “Vanya and Sonia and Masha and Spike,” a play by Christopher Durang that draws three of its title characters from Chekhov. A hit on Broadway, where it won the 2013 Tony for Best Play, the comedy is at the Charing Cross Theater through Jan. 8. The production, originally scheduled just as the pandemic took hold, is directed by Walter Bobbie, whose Broadway staging of “Chicago” recently marked its 25th anniversary.In Durang’s telling, Vanya and Sonia are no longer the uncle and niece of Chekhovian renown. Instead, they are siblings sharing discontented lives in rural Pennsylvania while their more glamorous sister Masha (Janie Dee), an actress, is off gathering toy boys like Spike (Charlie Maher).The cast of “Vanya and Sonia and Masha and Spike,” from left: Charlie Maher, Rebecca Lacey, Lukwesa Mwamba, Janie Dee and Michael Maloney.Marc Brenner The first half consists largely of extended chat about what costumes this trio should wear to a party: The spinsterish Sonia (Rebecca Lacey) isn’t sure whether to go as Jean Harlow or Marlene Dietrich, though we soon discover that she can do a spot-on vocal impersonation of Maggie Smith. The tone darkens, somewhat, after the intermission, with a series of monologues in which, as in “Uncle Vanya,” the characters address their psychic turmoil. “I’m worried about the future, and I miss the past,” says this play’s Vanya (a morose Michael Maloney), who turns out to be gay and is given to adoring the toned Spike in various states of undress.Dee’s feisty Masha has been married five times but isn’t beyond fretting about an outfit that doesn’t go down well with the locals: At such moments, the play lapses into the comparatively cheesy realm of sitcom (a genre unknown to Chekhov). Additional characters include Nina (Lukwesa Mwamba), the name referencing someone from another Chekhov play, “The Seagull,” and an emphatic seer named — you got it — Cassandra (Sara Powell). The literary forebears may be there, but the play doesn’t so much pay tribute to Chekhov as leave you pining for his wit and wisdom.After two shows that riff on (and in the case of the Durang, sometimes cheapen) an illustrious source or two, along comes Ralph Fiennes to give us the real thing, unadorned and unedited. The protean actor, rarely long absent from the stage, is directing himself in a theatrical performance of T.S. Eliot’s “Four Quartets,” at the Harold Pinter Theater through Dec. 18. The production, lasting 75 minutes with no intermission, represents a decidedly highbrow alternative to the japery on view nearby.Ralph Fiennes in T.S. Eliot’s “Four Quartets.”Matt HumphreyEliot’s masterwork was written in four parts while the poet was also evolving as a playwright, and Fiennes treats this writer’s often abstruse language as the stuff of drama, as potent in its way as the Shakespeare texts to which this actor regularly returns. I doubt I’m alone in not knowing what Eliot meant by the words “deliberate hebetude” from “East Coker,” the second of the quartets. But there’s no denying the mesmeric spell of a performer who can make even the opaque sound immediate. (I looked it up later: “Hebetude” means lethargy, or dullness.)Appearing barefoot, pausing to sip water or move the gray slabs that make up the designer Hildegard Bechtler’s elegantly austere set, the actor guides us through Eliot’s extended meditation on consciousness and hope, exploration and loss. Fiennes commits himself physically to an agile performance in which his body often writhes in response to Eliot’s images. And at a time when other London stages are filtering great work through a revisionist lens, here is the thing itself, ceaselessly and restlessly alive.Pride and Prejudice* (*sort of). Directed by Isobel McArthur and Simon Harvey. Criterion Theater, open-ended run.Vanya and Sonia and Masha and Spike. Directed by Walter Bobbie. Charing Cross Theater, through Jan. 8.Four Quartets. Directed by Ralph Fiennes. Harold Pinter Theater, through Dec. 18. More