Set in the 70’s when many people are fleeing from brutal totalitarian regimes to pursue their dreams in the land of freedom and opportunity, Australia. However, when—Communist agents—team up with corrupt police the ‘Croatian Six’ realise their nightmare has only just begun.

In stead of "when many people are fleeing from brutal totalitarian regimes to pursue their dreams in the land of freedom and opportunity, Australia" try:

"when Communist agents team up with corrupt police in 1970's Australia, ..."

Next, I would expect something along the lines of:

"a [main character description] must [main goal description]."

Hopefully the goal will clarify how the communists and police are antagonistic forces.

Good luck!

This is an interesting set-up for a story.

However a logline is usually told from the point of view of the lead character. It gives the character a goal and tells who or what is standing in the way.

I can't tell who the lead character is from your logline. Is it one of the corrupt police officers or possibly one of the communist agents?

I think this is a great idea for a story and if you focus on the lead character, your logline will better reflect your stories potential.

Hope that helps, good luck with this!