Island of Gnolls

The Island of Gnolls is not a fairy tale place; it definitely exists in northern Europe, more precisely – not far from Denmark. Legendary creatures – gnolls, descendants of trolls and gnomes – inhabit this secluded island.
By sheer coincidence, a resident of this distant island named Smuk ended up in the house of two brothers, Peter and Seb, and now he urgently needs help. The boys set off on a long and dangerous journey to the mysterious island to bring the gnoll home. Accompanying them is Peter's classmate, Isolde.
But if only it were that simple!
Gnolls turn to stone in the sunlight, just like their distant ancestors. So the kids will have to travel only at night, cross the strait on a magical ferry, hide from the terrifying jumpers, navigate through a nightmarish swamp and impenetrable jungles, and also look for the map of the Island!
Will the heroes manage to complete the task?
And will they be able to escape from the places where no mortal has returned?!