An apologia, playwright Alexi Kaye Campbell reminds us in his play so titled, is a defense, not an apology. With that in mind, would any play need an apologia beyond the words “Stockard Channing?”

You wouldn’t think so, and you’d be close to right, but Apologia, directed by Daniel Aukin and opening tonight at the Roundabout Theatre Company’s Off Broadway Laura Pels venue, could use some bolstering nonetheless.

Channing reprises a role she created in London, and we can mostly see what’s held her interest through the voyage. Her Kristin Miller is an irascible, razor-edged leftist and second-wave feminist, a 60-something, take-no-prisoners survivor of an era when being Germaine Greer was a viable career option.

Such trailblazing doesn’t come without sacrifice, though. Or, in Kristin’s case, sacrifices, to be more accurate. An art historian by trade, social critic by temperament and pioneer by circumstance, Kristin no doubt has lost much along the way, but on this night, as her loved ones (more or less) gather to celebrate her birthday and the recent publication of a memoir, only two sacrifices seem to matter: The damaged, angry sons who will come calling to confront and understand their hurtful, total absence from the life story Kristin has just written.

Dinner is going to be awkward.

Gathering at the ex-pat Kristin’s London home (it’s 2009, with a reference to Obama paving the way for a knowing “what happens next” joke) are conservative banker son Peter (Dancy) and his very Christian American fiancee Trudi (Talene Monahon); Hugh (John Tillinger), Kristin’s longtime gay pal and fellow fighter for the good; and Claire (Megalyn Echikunwoke), an ostentatious soap opera star and romantic partner of Kristin’s other son Simon (also Dancy).

The emotionally wounded Simon, rumored in the midst of a nervous breakdown, won’t show up until later in the night, after many secrets – and some red wine – are spilled.

In the meantime, Campbell indulges in the battleground dialogue that has each character taking sides on any number of issues – art versus commerce, rich versus poor, religion versus humanism, idealism versus pragmatism, youth versus experience. Underlying it all is the unspoken – temporarily, anyway – question of why, exactly, Kristin abandoned her sons when they were children, and why she has rendered them un-persons in her book.

At least, that’s how the still-suffering sons see it. Kristin insists the boys were taken by their father, but even she’ll concede she didn’t do much to get them back. She chose a different path, of political activism, of art, of work, and there wasn’t much room along that route for anyone else.

At least, that’s the zero-sum Sophie’s Choice that Campbell sets up here. Apologia suggests that, at least in Kristin’s day, women were forced into stark choices, and the play’s dramatic revelations hinge on some rather clunky situation-setting, all mirrored by Aukin’s sticky, stilted pacing.

Channing, who at least since Six Degrees of Separation has made art of the brittle intelligentsia, is a fascination, even when she seems a bit out of step with the production’s staccato rhythms (Monahon’s’s Trudi seems to have trained with Mamet). Dancy, like James Franco and Patty Duke before him, plays identical blood relations – which is not, be assured, the same as twins – and gets away with it as much as anyone can in the gimmicky situation. If the doublemint ruse in Apologia feels less than satisfying, it’s perhaps to do with a dinner party where one serving of mom-blame would have been plenty. Two feels a bit of a gorge.