If you've ever wondered just how deeply a new script depends on its actors, you would do well to see Tryst, now at the Merrimack Rep, which offers a kind of object lesson in how far two skilled performers can drive a vehicle that, if not exactly ramshackle, is nevertheless hardly a Rolls.

This is actually a retooled model of Tryst - after attending its unsuccessful British premiere, director Joe Brancato collaborated with author Karoline Leach on a new, more focused version, which has enjoyed considerable regional success before its current run at Merrimack.  And indeed, there's no doubt the chassis of the show is in good shape - the play turns on several dimes, in fact; the question is, where precisely is this particular vehicle supposed to be going?  That's what we can never really figure out.

Leach (along with the Merrimack's marketing department) clearly had it in mind to conjure a grim little entry in the familiar genre of the goth-romantic thriller - and in her first scenes, she seems at home in the idiom, and appears to know the lay of the land.  "George Love" (Mark Shanahan) is a manipulative cad who makes his living off the romantic fantasies of vulnerable Plain Janes in Edwardian England. He spots his prey by keeping an eye out for "“the sort of face that belongs to a woman who teaches piano or serves tea or issues library books." Only he scans for something else, too: "You’re looking for the little inconsistency," he explains. "The little something too expensive, too new, too nice for that face. The something that tells you it’s got a nice little nest egg. A few quid stashed away.’’ (Note that "it;" yes, Mr. Love has objectified women that far.)

Enter Adelaide (Andrea Maulella), whose thin visage fits that profile to a T (she works in the back of a hat shop, where "everyone has something wrong with them") and to whom George is soon smoothly whispering, "I cannot tell you how much I ache to take you in my arms." Seemingly swept off her feet, Adelaide agrees to an elopement at a remote seaside resort, all while being told, "Be sure to bring your checkbook." George's plan, of course - which he has carried off numerous times, he assures us - is to abscond with the contents of same after a night of love as Mr. and Mrs. Love (he's quite proud that he "always fulfills his responsibilities" in that regard).

And so far, so good; Leach's set-up is almost elemental, but she carries us to this re-imagined wedding night between Sweeney and Mrs. Lovett in spare but clean style. Needless to say, during their shared nocturnal climax we discover there's more to the self-aware Adelaide than met George's confidently appraising eye. But while it would be unfair to reveal the various twists in Tryst, it's not unfair to complain, I think, that in the end they don't amount to much thematically - and so don't quite satisfy the appetites Ms. Leach has so competently aroused in her first act. The playwright seems to be aiming for a paired set of psychological portraits, in which revelations are made by two personalities all but devoted to never revealing anything. This juxtaposition is intriguing, and at conjuring her characters' respective pains Ms. Leach is fairly successful - it's the integration of this psychological material into a steadily-developing contest of wills that seems to elude her. We intuit that she hopes for a rising sense that Adelaide's schemes may be nudging George, inch by inch, toward Bluebeard territory. But Leach's own schemes turn a bit clumsy, and her climax is far too abrupt for us to respond with the enjoyable shudder we're in the mood for.

Still, Tryst always holds our attention, even if it doesn't quite grip us, thanks to the polished and committed performances of Shanahan and (particularly) Maulella. Both have played their roles before, and both have their characters in their bones by now. And director Brancato knows just how to keep things moving - and us guessing - without overplaying his hand. All in all, Tryst wouldn't be a bad evening out for the kind of folks who read gruesome thrillers on the subway. But I think it will take yet another revision to make it something more.