The Mane Six go on holiday and at first everything seems rather boring.

Then a Rathian attacks the village they're staying in, burning all the boats and making it impossible to leave.
As there were no other ponies in the village to train, the Mane Six are trained in the art of killing monsters.
Accompanied by Rex, a monster tamer and his pet Great Jagi Fluffy, they attempt to make weapons and armour and then to take on the main threats of the island.