Director William Oldroyd’s “Eileen” is an equally captivating and frustrating psychological thriller based on Ottessa Moshfegh’s 2015 novel of the same name. It features the spellbinding duo of Thomason McKenzie and Ann Hathaway. It’s accented by the brilliant visual work from cinematographer Ari Wegner. And it features an alluring premise that mixes in an array of genres.

Unfortunately “Eileen” is held down by a sometimes clumsy and opaque screenplay. Adapted for the screen by Moshfegh and her husband Luke Goebel, the story starts a little messy but quickly evolves into something delightfully enigmatic and beguiling. Yet the script can’t deliver a satisfying payoff. The final act is riddled with holes in its logic. And there’s a good chance that anyone who has seen an episode of two of “Law and Order” will be picking the ending apart.

Set in the 1960s, McKenzie plays Eileen Dunlop, a mousy young secretary who works at a Massachusetts prison for boys. From the very start it’s obvious there’s something slightly “off” with her. But beyond that, she’s also a victim of her circumstances. She’s lonely and with no friends to speak of. She lives with her drunk and sickly ex-cop father (Shea Whigham) whose passive-aggressive cruelty is enough to mess with anyone’s mind. And she’s stuck in a go-nowhere job with no signs of opportunity.

But things change after the prison hires Dr. Rebecca St. John (Hathaway) to be their new psychologist. Rebecca is confident, beautiful, and vivacious and Eileen is instantly captivated. The more Eileen observes Rebecca the more infatuated she becomes. Soon she’s mimicking her new coworker – taking up smoking and coffee, dressing up as elegant as she can with nothing but her late mother’s clothes. And as a rather thinly sketched friendship forms between them, Eileen’s interest turns into full-on obsession.

At its best, “Eileen” is a sly and devious thriller with dashes of dark humor and even a tinge of Hitchcock. The off-kilter chemistry between McKenzie and Hathaway keeps us wondering what Oldroyd is going for. It makes for a good mystery, but he keeps the characters at an arm’s length. We never feel close enough to them to get a good sense of their feelings or (more importantly for a movie like this) their motivations.

The bigger issue comes in the final 30 minutes. The story takes a dramatic turn that’s meant to be both a surprising reveal and (I think) a shocking twist. Unfortunately it doesn’t make much sense. Our two main characters make several head-scratching decisions and their actions defy good sense. The ending is cloaked in ambiguity but not necessarily the good kind. Instead it leaves the movie in a far-fetched place. Oldroyd definitely goes for the jolt. What he delivers is more of a nudge.

“Eileen” has its strengths starting with the dazzling performances from McKenzie and Hathaway. The story itself is full of intriguing parts waiting to be pieced together. And the film is exquisitely shot, routinely impressing with its clever framing and evocative use of lighting and shadows. But in the end “Eileen” doesn’t seem sure of what it wants to be. Or maybe it wants to be several things. Either way, this diverting yet messy feature has a hard time sticking its landing. “Eileen” hits theaters December 8th.

VERDICT – 2.5 STARS