Most PI’s, whether real or fictional, find their jobs easier if they develop some sort of relationship with the police in their area. The PI/police relationship is mutually beneficial in a lot of obvious ways, so you would think it’d fall out naturally. But that’s not always the case. If you look at crime fiction, you see that while PIs and police do co-operate – sometimes very well – they are also sometimes at odds with each other. Sometimes it’s a matter of ‘patch wars,’ sometimes it’s a personal dislike, and sometimes it’s a perception of one side or the other as incompetent or worse. And sometimes it’s simply the friction you get with two different perspectives on the same case. But amicable, bitter or somewhere in between, the relations between PIs and cops make for an interesting layer in crime novels.

Arthur Conan Doyle’s Sherlock Holmes doesn’t dislike the…