>>> In my mind it was a small leap from one drug.

Except it isn’t. The Mexican cartels might traffic in cocaine to Australia [although I suspect the Colombian’s might do it directly themselves] because cocaine is grown in South America. So it’s a ‘local’ product. But your logline says heroin which is not ‘local’; the Mexicans have to import it from the Middle East like everyone else. And the shorter-cheaper-faster-less hazardous route to traffic heroin to Australia is via Southeast Asia.

>>> the DEA deals with drugs in the US not outside.

Ditto with the FBI. US law enforcement agencies do collaborate with other countries in terms of exchanging information, but the job of US law enforcement agencies is to worry about trafficing into the US – not into Australia.

On the other hand, if your FBI guy is a rogue agent, if he has gone off the reservation for some personal reason, a personal vendetta, if he his acting outside the bounds of his authorized jurisdiction — okay. But then, that makes him a more interesting character than the Australian home boy.

Quibbling aside, a logline should boil down to 30 words or less. The necessary characters to include are the protagonist and the antagonist. Who the protagonist gets as an ally may be central to the story, but it is a not usually a necessary detail in a logline

A necessary detail in a logline is the antagonist. Which is missing here. The logline identifies a “drug gang”, an antagonist group — but not an antagonist individual, the mastermind, the leader who serves as the “face” of the gang for the purposes of the audience.