Sight Unseen by Robert Goddard

A retired policeman decides to re-investigate a case he wasn't satisfied about, and collects a witness (the usual rootless single depressed middle-aged male) to help him. They wander around asking questions. People start being attacked, murdered, framed, committing suicide etcetera. We are really none the wiser as to why, even though some lost items turn up, until someone decides to Explain All to save someone else. Pretty forgettable.