Shadows in the Moonlight by Robert E. Howard

For a genuine Conan tale, full of barbarian craftiness, magic, fierce fighting and his berserker strength, this meets every criteria and is one of the best. Conan was raiding with the Free Companions when they were trapped and slaughtered by the merciless Shah Amurath the great Lord of Akif. Conan is one of the very few who escape by hiding in the mud of the marshes like a beast living on raw snake and muskrat. Luck, which seems to have deserted him, smiles again and allows him the chance for revenge and he eagerly seizes it, destroying his enemy with fierce strokes. Barely escaping his soldiers with the slave girl Olivia, once a princess of Koth, they reach a deserted island that holds many enchantments and strange dangers. Then the pirates arrive and things become even bloodier.