Siren, based on a seven volume manga by Yamazaki Sayaka, starts as your typical procedural: a couple of detectives (Matsuzaka Tori as Satomi Shinobu and Kimura Fumino as Inokuma Yuki), who are also a couple, investigate cases, make a very good team, etc etc. The only problem they seem to have is that they have to hide their relationship. But in a case were a hostess is killed, they meet Tachibana Kara (Nanao, sporting her characteristically unsettling and very very creepy smile), who seems to be interested in Yuki. She starts to follow her, puts a gps on Yuki's car, finds a place from where she can watch Shinobu's room, where Yuki expends most of her nights...
The series does a very good job on putting the basics of the story. We have three very good characters, played quite convincingly by the three actors (I always find Nanao a bright spot, even if she just seems to get the same roles over and over, as a very beautiful, slender and mean as hell woman), whose stories intertwine as Kara becomes closer and closer to Yuki, and raises Shinobu's alarm, as he notices something fishy. The atmosphere is also very good, darker than your typical Japanese TV series, and the show has some quite capable supporting characters (Osugi Ren, for example) who you will know from many Japanese movies and TV series. They even kiss, which is a rarity.
While the show keeps us guessing Kara's end game, we will be invested in the story, but, sadly, when we start to know more and more about her background and motives, everything starts to unravel, and not in a good way. The story loses itself in an unnecessary way, and, even if they were following the manga's story (which I haven't read so I can't say), it forces the plot to go to ways that will probably make the viewer lose interest. Which is a pity, as it's a waste of all the effort put before.
Totally worth watching, but knowing that the end will probably be a disappointment. Check it for the atmosphere, Nanao and leave thinking that the convoluted ending could have been avoided.
