Picasso and politics are a problematic theatrical mix; the great artist's "neutrality" in the face of fascism (followed by his vocal conversion to Communism) isn't the kind of thing that wins an audience's sympathy. Of course there's not much in his biography that could win an audience's sympathy, frankly; I've forgotten who first said that "Like life, Picasso was nasty, brutish and short," but that pretty much sums up the divine Pablo.

Of course by now there's no denying his work was often divine (although personally I'll always prefer Matisse), and if there's one thing you could admire about him, I suppose it would be his devotion to his own gift. Which playwright Jeffrey Hatcher has wisely made the crux of his two-hander A Picasso, now playing at the Merrimack Rep in a thoughtful production directed by artistic director Charles Towers.

Hatcher's conceit is that the great modernist has been dragged off the streets of occupied Paris for an interrogation by the Nazis in some dank subterranean dungeon, complete with Phantom-of-the-Opera arches, echoing footsteps and clanging doors. And his interlocutor has come straight from central casting, too - "Miss Fischer" (Kate Udall), a drily clipped power-fräulein in form-fitting Casablanca chic.

Her aim is to get the nervous artist to authenticate at least one of three sketches the Nazis have recently confiscated - although there's little doubt, actually, that any are anything but genuine Picassos.  So why is Miss Fischer so insistent on the artist's sign-off?  Well, it turns out she's organizing a curious kind of "group show" - one so hot it's going to literally burn, in fact.  (The Nazis did, indeed, execute public immolations of "degenerate" art.)  And once Picasso gives one of these works his blessing, she'll offer it up to the flames.

So far, so good, in what looks to be an elegant cat-and-mouse game over which work, precisely, must meet an untimely end.  And Hatcher's structure does offer a relatively sturdy frame for the playwright to skillfully drape a lot of art history and name-dropping - along with a quick sidebar on the meaning of Guernica; thus to many audiences, the script offers an entertaining tutorial; to the initiated, the recap may be less compelling, but at least it's painless.

The playwright does have one big - and good - twist up his sleeve, which I won't spoil except to hint that sometimes cats can secretly be in cahoots with mice.  Alas, the trouble with Hatcher's play is that its real drama only gets started after this big reveal - and then the playwright doesn't push his new premise nearly far enough before ringing down the curtain.  Indeed, the ironies that ripple out from the re-constituted situation he has conjured might have offered some original insights into the contradictions - and cruelties - that Picasso was famous for, but Hatcher seems happy to keep the artist firmly on the side of the angels, and with a bevy of quips at the ready, to boot.  (When he is told that Hitler is himself something of an artist, for instance, Picasso replies that yes, only he has a problem with borders.)

As it stands, Miss Fischer therefore emerges as the more compelling and complex character - and actress Kate Udall fully rises to the challenge of the role (and then some); after her wildly varied turns in A Moon for the Misbegotten, Four Places, and now A Picasso, in fact, I'd say Miss Udall has long since taken her place among Boston's best actresses (although you only get to see her in Lowell!).  Meanwhile, as the Great Man himself, Mark Zeisler - who bears a passing resemblance to Picasso - colors strictly (if subtly) within the lines of Hatcher's script, so we rarely get any sense of the artist's brilliant but destructive fire, even if the slow burn of the performance never entirely loses its intrigue.  Still, the impression left by both actors - and by their director, Towers - is that they're slightly spinning their wheels; A Picasso is an enjoyable trot through a particular episode of art history, but these thoroughbreds are capable of running a far greater race.