A pervasive feeling of dread runs throughout the first half of In Fear, a British horror movie from filmmaker Jeremy Lovering. Uneasy moans from the audience could be heard at the Sundance Film Festival screening I attended, as Lovering takes a seemingly benign situation and slowly tightens the screws.

Tom (Iain De Caestecker) and Lucy (Alice Englert), recently acquainted, are on their way to a music festival in Ireland. After stopping at a pub, Tom convinces Lucy to spend the night at the Kilairney House, an old hotel that’s supposedly somewhere nearby. Signs for the Kilairney House direct the couple through a maze of country roads. As the signs lead them in circles, Tom and Lucy begin to suspect that someone is messing with them. Before they know it, they’re hopelessly lost. The sun is setting. And they’re almost out of petrol.

It’s in the early going that Lovering really piles on a sense of foreboding. At a Sundance Film Festival Q&A he told the audience that the actors were unaware of the plot before shooting In Fear, that they weren’t given a script or a story. Lovering wanted to capture the actors’ genuine reactions, so he placed them in a harrowing situation, set up a few scares, and let the cameras roll. This “Blair Witch” approach pays off in the first half of In Fear, especially as Lucy begins to break down. Her fear is legit, and ultimately contagious.

But midway through the movie Lovering gives us an early peek at his hole card, and the tension, so cleverly sustained until now, begins to seep away. As the fear of the unknown is replaced with the fear of something more tangible, the movie loses its power. This may be the result of Lovering’s filmmaking style, which had him shooting 50 hours of improvisation and compiling In Fear in the editing bay. Perhaps if the movie was reedited to place the reveal closer to the end, Lovering could have goosed the tension even further. It’s hard to tell. These creative decisions don’t necessarily ruin In Fear, which remains a solid thriller with some hand-wringing moments. But by abandoning the tone he so carefully sets in the first half, Lovering misses out on making something great.