A young family experience supernatural happenings in their new home. After the family pet is butchered and the children have been attacked in their beds a non believer must play devils advocate to the deadly unseen evil by taking a life in order to save his families.

It sounds like you’re trying to dramatise the concept of doing the wrong thing for the right reason – we’ve had many loglines for concepts trying to do the same posted in the last few months. Seems to be a trend with a few premise variations in each case, but one thing that does repeat itself is the lack of believable stakes to motivate the character to take extreme action. In your case, he must kill and the question is asked why not just move away? In order to force someone to kill, you’de have to devise a scenario that absolutely leaves him no choice, like in the War of the Worlds re make when Tom Cruze kills the crazy guy in the basement to save his daughter. And as Rivhiev mentioned, is the whole film going to be about him deliberating whether or not to kill? Or will it be about him planning the murder? Or will it be about him covering up post kill? The plot is simply not clear.

First and foremost this is too long, you have to reduce the word count for the logline to work. In doing so, you’ll find that many of the descriptions are not needed, for example: the words “…young…”. and “…new…” can be cut from the first sentence and the words “…experience supernatural happenings…” can be replaced with ‘haunted’.

Other than that, you don’t need to detail the way in which the spirit terrorizes them, just describe a threat to their lives and the subsequent action the father must take. More importantly, though, you need to describe the main character sooner in the logline and using clearer terms – is he the eldest son, father or grandfather.