The Fallen Ones — Robert E. Vardeman; Victor Milan

The vagaries of the Destiny Stone, a magical amulet, have caused Princess Moriana and her lover Fost to lose the war against her powerful evil sister. And now, just when they could use a fairy godmother, they've got a pair of squabbling genies instead. As a last resort, there is always the Fallen Ones.

These repulsive, dangerous, reptilian aliens will help them, but there's a catch. The price is the retrieval of the awesome black diamond known as The Heart. All the Fallen Ones who have tried to steal it have died. Tsk, tsk. But perhaps the deadly rays of The Heart's guardian do not affect humans and genies. Who will be the first "volunteer" to find out?