The old confidence game always makes for a good plot, and in Karoline Leach’s excellent new play, “Tryst,” it’s worked to old-fashioned perfection. But suspenseful plotting is just one of the virtues of this two-character drama. It also boasts well-written characters, a deliciously gloomy Edwardian atmosphere, and a spellbinding performance by former Tony nominee Amelia Campbell.

The cat-and-mouse game begins with Dickensian aplomb: a storm, a dark-sounding violin, and a soot-colored street. Walls of wet black brick block out all light. A con man named George (Maxwell Caulfield) addresses the audience. He has a lower-class British accent and a dandy’s swagger. He doesn’t work for a living, he explains; rather, he goes about marrying unsuspecting old maids under a false name, robs them blind, and takes the next train out of town. But he considers it wrong not to make love to them; with George, they always get a wedding night.

Standing in her own spotlight, the homely, no-nonsense Adelaide (Ms. Campbell) tells her tale. She works in the back of a milliner’s shop – she’s not young or pretty enough for the counter – and lives with her parents. Buttoned up to the chin and prompt for tea, she upholds her class’s stringent morals. She has what George is looking for: a plain face, a desperate heart, and a diamond brooch.

As George and Adelaide’s alternating monologues give way to their playing scenes with each other, we see his preening sexual vanity set against her yearning for love. Then, remarkably, the picture shifts just slightly, and we see her vanity and his yearning for love.

Adelaide has her wits about her; she’s endured a hateful childhood and a demeaning job. It’s poignant to see the effect of the slightest hint of admiration on her lonely, shriveled ego, and more poignant still to see the pain on her face when she begins to question George’s motives.

Having whisked Adelaide away to a dispiriting hotel room for the honeymoon, George finds himself unaccountably moved by her fears and sorrows. He cannot steal her beloved brooch, and slinks back to the room to leave it behind. But just when you think he may be melting, he comes after her with vicious sarcasm, skewering her dream of opening a hat shop.

Few playwrights have Ms. Leach’s knack for bringing character to light in such an organic, unforced way: It is this ability that makes “Tryst” so fascinating and so affecting. In Ms. Campbell, “Tryst” has found its perfect Adelaide. There are layers within layers in Ms. Campbell’s brilliant performance. (Her vanity has an edge of pathos, and her shame has an edge of self-pity.) We oscillate among admiring Adelaide, pitying her, and being annoyed with her – which is to say that she feels like a real person.

Likewise, George excites a range of emotions between his cold-hearted entrance and his impassioned exit. Mr. Caulfield shows us George’s finessed exterior, his exterior hanging on for dear life, and finally his chaotic interior. When Adelaide thanks him for awakening her confidence, he cuts her off. “You don’t have to be grateful,” he snaps. “Be proud.”

By the end, she is proud – criticizing her employer up and down, and holding forth on her plans for a new and improved milliner’s shop. “I’m good, George,” she says, her eyes shining. “I’m too good for where I am. I’ve always been too good for where I am.” But in this dour world, hope only lasts for a few minutes.

Ms. Leach’s writing is economical and moving without ever being cute, and her pacing is near perfect. Her fine play, directed smoothly by Joe Brancato, is small of scale and large of heart. “Tryst” reminds me of what is missing from so much new theater: strong characters on a compelling journey, and a generous humanity that connects us with other people’s sorrows and dreams.

***

The central joke of “Show People,” the new play by Paul Weitz, is that out-of-work actors will do anything to experience the theater. Does the same apply to movie directors?

Mr. Weitz, best known for co-directing “About a Boy” and “American Pie” with his brother Chris, evidently yearns to see his work up on the boards. Apparently he’s untroubled by the fact that “Show People” feels like a rushed piece of writing churned out to meet a deadline.

The out-of-work actors who will do anything are the brassy Marnie (Debra Monk) and the geriatric Jerry (Lawrence Pressman). They’ve been hired by a rich young Turk named Tom (Ty Burrell) to impersonate his parents over a weekend in Montauk, where Tom plans to propose to his girlfriend. The premise is promising, and Mr. Weitz and director Peter Askin milk some laughs from Jerry’s commitment to character and Marnie’s more mercenary approach to the job.

“Show People” has most of the important elements in place. There are smart costumes by Jeff Mahshie and a smashing set by Heidi Ettinger. Mr. Burrell makes a great whiny man-boy executive, and Mr. Pressman has charm and comic timing in spades. Peter Askin has a nice way with the staging.

Some good things also fly off Mr. Weitz’s pen. Particularly memorable is a scene in which the exasperated Marnie gives Tom’s girlfriend, Natalie (Judy Greer), an acting lesson. As Marnie, Ms. Monk delights the audience with her purrs and wisecracks. She’s a great would-be diva and a damn good actress.

But Mr. Weitz’s underdeveloped script has to resort to a series of quick fixes no better than the old TV series’ standby “it was only a dream.”Without a solid comedic structure to fall back on, Mr.Weitz just tries to keep dancing as fast as he can. As a Hollywood director, he ought to know better than anyone: “Show People” could be really good after a couple more rewrites.

“Tryst” on open run (2162 Broadway, 212-580-1313). “Show People” until April 30 (307 W. 43rd Street, 212-246-4422).