An elf turns evil and starts ruling this world's hell. His sister is sent to assassinate him.
In other parts of the world, a village of halflings is either attacked by or witnesses a dragon. Daughter of the village chief goes missing, who sets out to rescue her.
The Chief (who is by profession a woodcutter, the halflings are known for dealing with special kinds of woods) meets and creates a group of adventurers.
The Chief's daughter in hell dimension finds an imprisoned man. The two of them manage to escape and are now fleeing the hell dimension. The chief and his party get into the hell dimension. The man with the chief's daughter discovers that he has the power to turn into a demon. They escape the dimension.
The Elf ruler of hell dies, a golem which he created takes over. Chief's group of heroes are in the capital city. City gets attacked by a dragon. Golem appears in city, slays the dragon together with other heroes. The chief's daughter and the man she escaped with fall in love.
If anyone remembers this plot, please I have been looking for this novel/series for ages. When I read the book some years ago it was in German, meaning that the book either must have been translated or was originally written in German.