Beyond the Barrier Reef. Christopher Cummings

Sixteen-year-old navy cadet, Andrew Collins, is spending the April school holidays with his older sister, Carmen, assisting a university research program on the Great Barrier Reef.
Whilst SCUBA diving hundred kilometres out to sea around Yule Reef, they find something out of place, something unnatural that should not be there… and that they should not have seen.
The discovery leads brother and sister into the most desperate situation they have ever encountered. Join them as they struggle to survive in the harsh and unforgiving environment against both nature and an evil cartel.