Don't Knock Twice for the most part is a horror film I truly enjoy. What it lacks in originality it compensates with good old horror basics where the emphasis lies on buildup of atmosphere, tension and dread. Less is more. In the whole film there are like two or three jump scares and when they happen they matter.
I can't tell you how refreshing this is since nowadays a lot of film makers seem to think that every horror films needs to be filled with jump scares and ultra violence. Of course you have different types of horrors and I myself do like to indulge myself with those gory and bloody films. But what if you could the best of those types into one film? Only a few have succeeded and unfortunately Don't Knock Twice doesn't fall into this category. However it is one that is very close to the Insidious films where dread is just as important as scary and creepy imagery. And to be honest they can't make enough of them. I like the more slower and mystery based horrors where not everything is what it seems and where many different outcomes are possible. This film certainly does it's best to make you doubt the main characters since both of them are troubled in their own way. Katee Sackhoff was really good as a somewhat unstable mother who gave up her daughter Chloe (played by Lucy Boynton) and now some years after she gets to take care of her again. At first Chloe didn't want anything to do with her until she gets into trouble and is scared out of her wits. This isn't a case where it is clear who is good and who is not which really adds a healthy amount of suspense. Actually the film plays around with certain subject and themes without making it too obvious of what is going on.
Then after the first hour the film derails and becomes quite messy. It completely downplays the horror and then let's the crime / murder mystery take the upper hand in a way they do in every predictable crime film devoid of any thrills and atmosphere. Forget about creepy or scary moments. Still the last two minutes do redeem this messy half hour although if you had been paying attention is predictable and a little lazy if you ask me. All this time Don't Know Twice was filled with promise and it seemed to be delivering and then nothing. Not entirely disappointing but considering how close they were it does feel as a slight letdown.
But overall the good elements more than enough outweigh the bad ones and certainly make this one worth your time especially if you are a fan.