Jesse Wilson 
Commander Rex and the Black Unicorn [EPUB ebook] 

The unicorns are returning.
A prophetic event heralds the return of the Black Unicorn: a mythical beast banished by the Gods ages ago. 
Commander Rex and his team is summoned by King Lexam to investigate the cause of this strange event. The unlikely unicorn hunters don’t believe in the Black Unicorn at all, but when summoned by the king, you don’t say no.
But soon, it becomes clear that there might be more to the events than just a prophecy. They must find who is responsible… and fast.