This is the 7th Gervase Fen novel by Edmund Crispin.
A young actress, Gloria Scott , drowns after throwing herself off Waterloo Bridge. The news sends shock-waves around the film studio at Long Fulton where Gervase Fen, Oxford Don and amateur criminologist, happens to be working as a consultant on a bio-pic of the life of Alexander Pope the poet ( https://en.wikipedia.org/wiki/Alexander_Pope ) . With help from his friend, Inspector Humbleby, this tragic loss of young life leads them to many more dark places – Ms. Scott’s room has been searched and all signs of her real identity have been removed. Mere minutes before Humbleby interrogates her co-workers, one of them, a lecherous cameraman, is poisoned and more deaths are to follow.
This novel is set in a world that Bruce Montgomery (the real person behind the nom de plume of Edmund Crispin) knew well as a professional composer most often of film music (see http://www.imdb.com/name/nm0599736/ for a full list of the 32 films he worked on from 1949 to 1966 – 1961s Raising the Wind, a broad comedy, is an especially interesting film for fans of his novels as he wrote both the screenplay and the score for this film from the Carry On directing/producing team with a cast of classic British film comedy stars)
This does seem to be the Fen that people seem to be most divided over with some disliking it intensely – the usual criticisms are (1) the absence of the killer for most of the novel – he/she appears in person or by letter only at the beginning and end, (2) that Fen tends to stay in the background for much of the book and (3) the comedy is too much in the foreground.
Personally this is one of my favourite Fens precisely because of there is a more sophisticated level of humour than with some of the other Fen books mostly throughout (the start is a bit iffy from a humour perspective) and the fact that Fen has to act as an observer here because this is a world that is quite distinct from his usual intellectual milieu so we see what he sees. There are crimes but I am not sure it can really be classed as a pure mystery.
This is almost the end of the run of Fen novels in the 1940s and 1950s, The Long Divorce followed in 1952 along with some short short stories collected in Beware of the Trains (1953) and Fen Country (1979). One more novel appeared in 1977 – The Glimpses of the Moon – but Crispin/Montgomery turned to reviewing, editing anthologies (mostly of SF but there are 2 good Crime/Mystery anthologies) and writing Film Music (at least until the mid-1960s) – see David Whittles Bruce Montgomery/Edmund Crispin: A Life in Music and Books for more details of his life.
I aim to complete my reviews of the set of Fen novels and short stories at some point in the future.
 Presumably the stage name of the actress is an homage to “The Adventure of the Gloria Scott” by Sir Arthur Conan Doyle, collected in The Memoirs of Sherlock Holmes