Kimihiko Kimizuka has always had a predisposition for running into trouble. He has stumbled into so many crime scenes that the police started to suspect him. So when one day he is asked to take a suspicious suitcase on board a plane he doesn't even question why. Once he gets on the plane and sits down a voice asks over the speaker if there happens to be a detective on board. The girl next to Kimihiko stands up and says that she is a detective. She then turns to Kimihiko and asks him to be her sidekick. Kimihiko decides to go along with her, even though he still had his questions regarding the situation. The girl says that kimihiko can call her by her code name, Siesta. As they walk away from all the passengers they learn that the plane has been hijacked by a mysterious man who uses the code name Bat. He tells Siesta and Kimihiko that he will let everyone go if they are able to guess the reason that he hijacked the plane. After talking about themselves Bat lets it slip that he has too much time on his hands. Siesta deduces that the reason he hijacked the plane is because he was bored. Bat admits that she guessed correctly but he still starts a fight. As kimihiko wonders what to do he rembers the case that he was asked to bring as a carry-on and throws it to Siesta who breaks it open and reveals a gun hidden inside. After the fight is over she tells kimihiko that it was no coincidence that they were on board together. She also admits that she was the one who arranged for him to bring the case onboard. After that Siesta asks for him to continue helping her. And thus begins their three year adventure together.
The Detective is Already Dead was more interesting than I thought it would be. While things don't happen in chronological order you still get an idea of what happened in the past with flashbacks. The majority of the season stays clean. There is a short shower scene in the last episode though. Overall, it wasn't my favorite mystery anime, but it was definitely worth the watch.