Sally A. Laughlin 
Mystic Moon Warriors [EPUB ebook] 

On a routine patrol that turns out to be anything but routine, police officers John ‘Mac’ Mac Quinn and Kessyndra ‘Kess’ Tamer are brought through a portal into the magical world of Mystovia, inhabited by Amazons, Elves, Sorcerers, mythical creatures and demons.
After one of Mystovia’s powerful Crystal Orbs, lost for many years, is found by a terrorist, he quickly discovers the magical potency of the artifact he possesses.  Undetected and unhindered, he would be able to move between the two worlds and carry out his schemes not only on Earth, but in Mystovia as well.
The officers embark on a perilous journey to save the realm. Plunged into unknown danger and facing a demonic horde, they soon learn the real reason why they were chosen to be brought into Mystovia.