Harold and Maude

I read this with the assumption that it was the book the film was based on, not the other way round. It's a fine novelisation but doesn't add much.

Apparently, the book is based on Higgins' own screenplay, which was made into the movie. There are only miniscule differences between the book and the movie (and at 100 pages the book is rather short), so there is really no reason to read the book, though it is not bad at all.

Watch the film instead, and be a happier person forever.