BEYOND THE BRINK

Jack, volunteer Game Ranger and loner by choice since experiencing a personal loss, has his life turned upside down when he rescues two alien children from the clutches of Rhino poachers. Communication is a huge issue, so finding out where they came from is a mission in itself.
When he does, humanity has its first real contact with an alien race who have come to offer assistance to Earth against an impending invasion by another aggressive race.
However this comes with a caveat, unless the majority of Earth's nations agree to the terms they will leave and our planet will be at the mercy of a race that regards us as primitive and expendable.