One day, a worker at a construction site found a skeleton and two ruby ​​rings. However, one was stolen by the Puma Gang, an international smuggling ring, and the other by the Moonlit Birdman. And before the Moonlit Birdman, who has even stolen the second ring from the Puma gang, is private detective Goro Shiina, also known as Hammerkit. Hammerkit and the Puma gang chase the moonlit birdman. What is the secret behind the ruby ​​ring that they desperately fight for?