The Decagon House Murders by Yukito Ayatsuji

The members of a university mystery club decide to visit an island that was the site of a grisly, unsolved multiple murder the year before. They’re looking forward to investigating the crime, putting their passion for solving mysteries to practical use, but before long there is a fresh murder, and soon the club members realise they are being picked off one by one. The remaining amateur sleuths will have to use all of their murder-mystery expertise to find the killer before they end up dead too.