Early Albert Campion adventures are a lot of fun. _Look to the Lady_, _Mystery Mile_ and _Sweet Danger_ are all great reads. They are not mysteries in the sense of Christie or Carr, and combine all sorts of elements, including touches of Wodehouse and Buchan.
Most of them are told from someone else's viewpoint, but _Pig_, while a great mystery story, is told first-person by Campion himself.
There is a reason Dr. Watson characters tell stories about great detectives. The detective is half-prestidigiator (cf. the great detectives of John Dickson Carr). When clues come the detective's way they make the case clearer to him, but when they are presented to the reader through Dr. Watson characters, they tend to mystify the reader further. It is considered "fair play" to present the reader with all the clues as they become available, although it's fair for the author to misconstrue what they may mean via the interpretation of the detective's less astute assistants.
Since Campion is telling the story himself, he has to mystify the reader by not fully describing clues or neglecting to explain to the reader how these clues fit into his overall reasoning. This sometimes makes it seem like Campion is playing a trick on the reader. The story would have been done much better through the eyes of another character.
Nevertheless, the (very short, perhaps too short) novella is solid and a lot of fun, with intriguing characters like Hayhoe, Gilbert Whippet, the officious Reverend Bathwick, and R. I. ("Pig") Peters, who simply refuses to remain dead.