Please suggest me a crime novel (mystery, thriller) where a protagonist takes up the investigation of a previous investigator who was killed because they got too close.

As per title. I'm looking for a crime novel (mystery, thriller, spy) or fantasy where an investigator gets killed because they get too close to unravel a conspiracy/a crime (bonus point if no one knows that's the real reason) – then the protagonist takes up the mantle (bonus point of protag has no idea about the conspiracy/crime at first).

Many thanks.