Somewhere in the great ocean, lies and island that is not present on any map. Its inhabitants are those who first accidentally stumbled upon its shores. And they have called it their home ever since, all the while making sure that no one else is to enter the island and ruin their way of life.
Just recently, a travelling party ended up finding the entrance to the island. It turns out that the party belonged to a group of
"new land seekers" in service to a greedy king. that king has now sent masses of his imperial army to come and claim this island to be a part of his kingdom.
It mow falls into the hands of the settlers of the hidden island to defend their home. The path to the island is an unnatural valley between the waves of the ocean, the settlers have already built some sort of fortifications but it will take great courage and immaculate planning to be able to hold off the king's armies.