This is book 6 of the "Gervase Fen" series.

This note contains spoilers for the book.

Ended up reading this upstairs, in parallel to other things, for a while, then eventually just finished it.

Prof. Fen decides to run for parliament, and runs into a Situation in the district he's running in (nowhere near home; apparently they don't have anything like our residency requirements for MPs. Then again the whole country is about the size of one of our states.)

Features an actual escaped lunatic—who did not harm anybody in this book. Apparently the NHS sent him to the wrong place, which wasn't equipped to secure him adequately.