Killed Again, Mr. Detective

Harvey was found impaled on an object in the mansion, his lower body missing.
Who had brutally murdered him? In the midst of the storm, a sound like singing echoed. It reminded everyone of the "Siren," the fairytale creature that Harvey had been pursuing, and they all held their breath. At the same time, Luciola was found unconscious. When
Luciola woke up, she told Sakuya and the others about the attack and said it was the work of a Siren.
After hearing Luciola's story, Sakuya noticed something strange.

Just as they uncover the truth behind Harvey's murder, another murder occurs.
Shardina suddenly appears and gives Sakuya a deadline to solve the case.
If it's not solved by 6 AM the next morning, the island will be bombed with missiles.
They head to the crime scene, but Dmitri's body is nowhere to be found.
All that remains is a large pool of blood, a scarf, and the word "Siren" written in blood on the wall.
Sakuya and his team continue their investigation, but more victims appear...

In search of clues to the case, Sakuya enters Eliseo's studio with Shardina.
All they find is Eliseo's diary. It contains details about Eliseo before he became a painter, and, surprisingly, a secret related to his immortal body.
As the time limit set by Shardina approaches, Sakuya slowly gets closer to the truth.
The series of incidents are deeply connected to events in Eliseo's past.
The perpetrator of the inexplicable serial murders is...

It was Luciola who killed Dmitri and Ivan.
Luciola is now trying to kill her final target, Katia. Sakuya tries to persuade her, but at the same time, the time limit declared by Shardina arrives. Missiles rain down on the island.
The mansion collapses, and Sakuya and the others fall with the collapsing ground.
Will Sakuya and the others be able to escape from the island...?