Spears of the Sun

It's not that Jules looks for trouble. As an astrobiologist, he'd rather study the intriguing alien plant/animal species, Blackroot. But his telepathic abilities attract the wrong aliens, and Terrans. This time it's General Ki Rowdinth, crazed leader of the Vermakt people. The psychotic tyrant intends to extort the combined gold depositories of Earth and all the colony planets to finance an army that will rule the worlds. If the Worlds Government doesn't agree to Rowdinth's demands, he vows to engage a dark-energy weapon that will destroy Earth.

It looks as though only Jules, with his powerful telepathic abilities, stands between the rat-like general and the total annihilation of our homeworld.

The third book in Jean Kilczer's Star Sojourner Series, Spears of the Sun is a standalone novel and can be enjoyed even if you haven't read other books in the series.