A powder-keg plot setup triggers an underwhelming display of dramatic fireworks in "Z for Zachariah," a post-apocalyptic survival tale propelled by male-female emotional dynamics. Set in a remote valley spared from radioactive contamination after a presumed global catastrophe, the film from director Craig Zobel effectively sets all its surface parts in motion but, crucially, doesn't sufficiently develop the turbulent undercurrent of tension and intrigue that are called for in the hothouse circumstances. This, despite the solid efforts of the only actors in the piece, Chiwetel Ejiofor, Margot Robbie, and Chris Pine.
Based on the 1974 novel of the same title by Robert C. O'Brien, the film does possess something of that last-days-of-man-on-Earth feeling of numerous sci-fi ventures of that period. The film begins with a young woman and her dog emerging from a contamination-proof suit on high ground above what is otherwise apparently an unlivable world.
For her part, Ann (Robbie) has self-sufficiently persevered. She lives in the spacious rural house where she grew up, is surrounded by thousands of books and LP records, and industriously tends to her crops. She even has a cow that gives milk and finds solace in religion, playing the organ in the small chapel nearby that her preacher father built. She's also quite a beauty, not that it matters. Not at the moment, anyway.
All this changes with the startling arrival of a man who also emerges from a protective suit, but in hysterics and desperately afraid of contamination. This is John (Ejiofor), who, after the initial moments of mutual alarm have passed, accepts Ann's hospitality and takes to a bed to recover. A research scientist who claims to have designed the resistant suit, he soon applies his expertise to getting her freezer and tractor working again and eventually works out a plan to build a waterwheel to generate power.
What are a man and woman going to do together to pass the time if they believe they're the last two people on Earth? Despite the obvious answer, this pair proceeds slowly. Having achieved a certain intimacy while Ann nursed John back to health, they eventually share a romantic dinner at which she gets tipsy and pushes things to the brink of sex. Surprisingly, John puts her off, insisting that going further would change everything and that they should take their time.
No sooner does this cooling take place than a third wheel turns up to change the dynamics entirely. Caleb (Pine) is a scruffy young guy with traces of radiation on him, but the other two agree to let him stay for a bit. The men sniff each other out about their mutual intentions, of course, but the situation seems defused when Caleb agrees to help John finish the big project of building the waterwheel.
However, even if the men decide that they can co-habit, Ann is eventually going to have something to say about it, leading one to suspect that one-third of the world's known human population won't be around that much longer.
The effectiveness of the piece, especially in its final half, is almost entirely dependent upon subtext, mutual suspicions, underlying tensions, sexual tipping points, self-control, and all manner of other human impulses that lie just beneath the surface. Unfortunately, screenwriter Nissar Modi and director Zobel don' t manage to draw these out in a palpable way so that the drama really flattens out during the climactic stretch on its way to a very ho-hum conclusion. Where the blame for this truly lies is difficult to gauge, but another factor here is cast chemistry; on a moment-to-moment basis, the three actors seem entirely engaged with their roles, but the electric currents between them are not strong and constant.