Unknown Male by Nicolas Obregon is the second in the Iwata series, it is worth starting with the first in the series Blue Light Yokohama.
Skye Mackintosh, a young English student is found brutally murdered in a “love” hotel in Tokyo. Several prostitutes have disappeared off the streets with no trace. How are the two linked?
Iwata has been away from Tokyo for a decade after the Akashi case (Blue Light Yokohama) he is summoned back by his old commander to lead the search for the murderer of Skye assisted by Anthea Lynch, a detective sent to Tokyo by the Met police who also has some skeletons in her closet.
Combine the twists and turns of a murder investigation with a truly chilling serial killer and Iwata’s struggle for resolution with his long estranged father and you get a cracking novel.