With a tip-off that the demented serial killer Joohyun is hiding out on a deserted island, Detective Seoyoon heads to the island. However, the island turns out to be swarming with strange creatures that are half-human, half-fish. Seoyoon is left without any choice other than to work with the serial killer to escape the island. Would she be able to make an escape? What has happened on this island?

Heukgwi-do, a deserted island surrounded by damp gray fog. Upon getting a tip-off that the serial killer Joohyun is hiding on the island, Seoyoon and Kim head to Heukgwi-do. While looking for the traces of Joohyun on this ominous island, the two suddenly encounter strange creatures who are half-human and half-fish.

Seoyoon and Kim struggle to death, fighting off the creatures. Kim gets mercilessly killed in the fight and Seoyoon tries to run away only to be fully besieged. Just when she is about to give up everything, someone saves her life. Thanking her savior, Seoyoon slowly sees at her face… and it’s Joohyun.

After a dogfight, Seoyoon finally overpowers Joohyun and puts handcuffs on her. But soon, an old shack they are hiding in is starting to crumble by the strange creatures. Seoyoon decides that she cannot handle this situation alone, so she uncuffs Joohyun and their combined operation begins to get out of the island alive.

Maintaining an uneasy alliance with Joohyun, Seoyoon struggles to find an escape. However, the harder she tries, the deeper she falls under the secrets of Heukgwi-do. Finally, she faces a colossal truth beyond imagination and horror. In the center of it is Joohyun.

Would you believe me if I told you there was an island that worshipped mice until the mid-1970s in South Korea? Gal-do in Tongyeong did.
Gal-do was often referred to as Pirates Island because of the frequent fights between its residents. Googling the old articles would reveal incidents such as a secret burial of an orphan, a missing teacher couple, and mass violence due to generational conflict. In 2003, after Super Typhoon Maemi hit the island, the residents left the island, making it a deserted island.

The strangest fact about Gal-do is that the people worshipped mice. Despite the chronic food shortage, the islanders did not hate mice that chipped away the harvest but treated them as gods, even practicing a grand worshipping ceremony every three years. What a mysterious custom for this modern age!

They had probably tried to fight the mice at first. But killing mice after mice did not stop them from bothering the islanders. Then came a sense of helplessness coming from the realization that humans could control or even understand nature no matter how they tried. Perhaps, this underlying fear ushered them into worshipping mice as gods.

Gal-do fuels imagination. When did people start practicing the worshipping ceremony? Did they really leave the island because of the typhoon? What strange things have happened on this island? These questions created Heukgwi-do, with a touch of cosmic horror—a fear of helplessness in the face of unbeatable, incomprehensible, and mysterious beings.

There’s more. While we get closer to the secret of the island, a refreshing buddy action unfolds, led by two female leads. Our two heroines, respectively practicing fencing and boxing, take down numerous strange creatures in so many imaginative ways, in the mud flat, in the cave, and over the cliff.

So to speak, Black Turtle Island is a story where you follow a whirlwind of entertaining female action and, before you know it, encounter a cosmic horror universe.