The Detective Is Already Dead, Vol. 5 (manga)

"Now we know what we're up against…!" With a little help from Charlotte Arisaka Anderson and a surprise appearance by the late detective herself, I, Kimihiko Kimizuka, was able to defeat the devious pseudohuman Chameleon who attacked us during our cruise ship investigation. That doesn't mean the end of our excitement aboard the ship, though, because right after cleaning up that mess, Charlie, Yui, Nagisa, and I were summoned to…learn the truth about Siesta's death?! Not only that, but it turns out Nagisa has some bigger shoes to fill than we thought… What exactly was the ace detective wrapped up in before her untimely demise?!

Volume 5 of The Detective Is Already Dead manga series by nigozyu.