When a trailer is more capable of disturbing the audience than the actual film, there’s a problem.

“My Cousin Rachel” — written and directed by Roger Michell (“Notting Hill,” “Morning Glory”) — is a dark romance film based on Daphne du Maurier’s mystery romance novel of the same name that unfortunately falls into this category. After watching the film, one would be hesitant to call it dark — tame might be a better label.

Philip Ashley (Sam Claflin) is raised on the estate of his endearing cousin, guardian and bachelor, Ambrose Ashley, who never needed the presence of woman. Yet as Ambrose’s health declines and he leaves to Florence, his letters to Philip reveal a newfound infatuation — his cousin Rachel (Rachel Weisz). But his attraction mutates into torment as he writes, “she’ll ruin me.”

All of this background is hastily packed into the pre-title sequence.

When Rachel suddenly materializes in England — as soon as Philip learns of his cousin’s death — he’s set on retribution, convinced she was largely responsible. But  Rachel’s allure is spellbinding , and as soon as they’re in the same room together, Philip can’t help but adhere to the usual English formalities and share a cup of tea with her.

Thus begins the constant twists and contradictions as we attempt to decipher the mysterious woman and her true motives. The same questions that plague Philip leave the audience locked in a persistent mind game. Is their budding relationship a pretence for Rachel to inherit Philip’s wealth? Did she kill Ambrose? Evidence points us in every direction.

As a mystery, the film largely succeeds. Weisz deftly creates a character hard to read. She has this uncanny ability to put on a lissome performance that suggests both manipulation and genuine emotion. At the very moment we are convinced of Rachel’s malicious intent, she regains all semblance of innocence.

Claflin also plays a palpable inexperienced country boy, as he, like the audience, bends along with every one of Rachel’s moves.  There is a back-and-forth tension that remains consistent throughout the film. At one point we no longer know who is really in danger — is it Philip or Rachel?

Alice Normington, production designer, and Mike Eley, cinematographer, complement each other to portray a decaying Gothic world set in Victorian England as we traverse from lifeless cold forests to dimly lit, musty rooms.

But beyond that, the film loses its luster.

With the ambiguity Michell maintains throughout “My Cousin Rachel”, he also sacrifices any chance to explore Rachel in-depth. Who is Rachel? It’s a question that drives the entire film, but it is asked ad nauseam — to the extent that one quickly loses interest in even bothering to ask.

If she has to take on multiple identities, then there’s a great opportunity to explore this duplicity — is she the “woman who’s making her way in the world as she wishes” or a murderer? Maybe that’s the point. But Michell forfeits any chance to flesh Rachel out.

And just as the characters teeter back and forth, the movie is afraid to commit to any one genre – is it a romance, thriller, or both?

It founders in its attempt to be the thriller it is marketed as. The house seemingly appears to grow more and more dilapidated, with accentuated shadows and low-lit environments that feign the perfect gothic thriller — but the suspense never moves us in our seats. At times, it feels like an unconvincing romance.

“My Cousin Rachel” is a tease at best. And that’s the most unfortunate part, because it has all the potential to be an exciting dark romance, thriller, mystery or all of the above. Rachel could be like the 19th century Gothic version of Amy from David Fincher’s “Gone Girl.” But she’s never truly feels like a threatening or formidable presence.

At most, Rachel is only as terrifying as the tea she might have poisoned. Perhaps this can be threatening, depending on how much you need your cup of tea.