In the Moons of Borea
(Cthulu Mythos, Book 5)
by Brian Lumley

Description:
In this book Lumley continues his fantasy/horror/SF/adventure series by following the adventures of two colleagues of Titus Crow: his friend Henri De Marigny and telepathic Hank Silberhutte.

In "Spawn of the Winds," Hank ended up on Borea, where Ithaqua is master of most of the world. And he is married to Armandra, Ithaqua's human daughter (who opposes her father's rule).

Then De Marigny, still learning to use the "time-clock," inadvertantly ends up on Borea --- and in lots of trouble. When the time-clock is stolen, he and Hank embark upon a strange quest among the moons of Borea:

Numinos! Settled by Vikings who worship Ithaqua as a god. But there is an island, shaped like a star-stone, where Ithaqua cannot go.

Dromos! Ice-moon, inhabited by ice-priests from ancient Theem'hdra, millions of years old and wise in the ways of evil. Possibly even Ithaqua fears these creatures who once were men.

And what of Armandra, who fears that Hank will leave her and return to Earth if they should recapture the time-clock?

This may be a horror novel but it is also a tale of adventure as small bands of humans try to survive against the might of evil Ithaqua and his followers.