One of the most impressive aspects of Denis Villeneuve's movies is the way he crafts, not just moody atmospheres, but true character portraits, no matter the setting. It's why Dune, for all its scope, is able to needle down and connect us emotionally to such a big cast, and why Arrival smartly pulled off a story about human infighting amid an alien invasion. Notably, it's his 2013 film Prisoners that achieves one of his most cerebral stories ever, focusing on fathers searching for missing daughters. However, by the time the film wraps, it's clear its most heartbreaking arc isn't the kidnapping one, but the one focused on the rescuers.
Hugh Jackman's Keller and Terrence Howard's Franklin are left searching for their girls, Anna and Joy, respectively, kidnapping the socially-awkward Alex as they think he's the culprit. It resulted in Detective Loki (Jake Gyllenhaal) trying his best to crack the case as he could tell the men were holding secrets and going over the line in their brand of vigilante justice to discern the truth.
In so doing, Keller's relationship with his family crumbled as he became a drunk, obsessed and lashing out at everyone. It got even worse when Franklin's girl escaped, making Keller feel like a failure who couldn't overcome a weak police system in their desolate Pennsylvania town.
As fate would have it, it was actually Alex's foster mom, Holly, who was secretly using Alex and another dead adoptee, Bob, as kidnappers. She preyed on their weak minds to snatch girls as she was bitter she lost her child to cancer.
Holly wanted to create monsters out of parents, using this grief to stick it to God, as she lost her faith and wanted everyone to suffer. Eventually, Keller gleaned intel from Joy and went to accost Holly, only to end up drugged and locked in a sandpit under her home. Loki visited and managed to suss clues out, killing Holly and freeing Anna, but the thing was, by that time, they assumed Keller was dead.
Loki had no clues on the father, with even Keller's own family accepting if he showed up, he'd face jail time for torturing Alex. It felt like a big betrayal, as Keller was desperate, trying to be his child's hero, but as the movie ended, all he got was a prison to die alone in. It was such a sinister cliffhanger, with Keller finding his daughter's whistle, blowing it and Loki faintly hearing it above ground. Still, Loki just turned back to wonder what was the sound, with the backdrop of crickets and the cold rushing air around.
Prisoners then cut to the credits, leaving fans debating to this day if Loki found Keller. It's twisted to end the story like this because Keller would easily go from captor to deceased if Loki left the residence. It's all because he did what any father would do in what's ultimately one of cinema's cruelest and most punishing fates. It was so crushing and unfair for Keller to go so far and not get to see or know his child was reunited with loved ones, and that Anna got no closure on the man who'd move mountains for her.