I disagree with the previous post.
The structure of a logline needs to be similar to that of the plot i.e: Inciting incident then MC then goal. In the best loglines the read emulates the emotions the story will evoke via a similar order of action and description.
This logline is too long and uses too many words to describe superfluous story elements. No need to name the race of monsters best to use the precious logline real-estate on describing them instead.
No need to mention that the human race inhabits the Earth this is intrinsically understood.
Are there knights in Australia? When is the story set? Modern day or 200 years ago? I'm not sure there even were knights per say 200 years ago when Australia was first colonised but if set in modern day then perhaps make him an army sergeant or general.
All war is devastating no need to mention this in the logline in addition to the fact that devastating is too generic a description to be effective in a logline.
What does "...drag the world back from darkness." mean?
Did the monsters block out the sun? Or is this a figure of speech?
Best to be specific in these descriptions, what will drag the world back from darkness actually look like?
If I were to boil the story down to its bare components it would look like this:
After a race of monsters from beneath the Earths crust wages a war against humanity a rogue general finds the solution to stopping the war in an aboriginal boy they must fight the monsters leader together.
Hope this helps.