EVAN FIELD is the pseudonym for two New York writers on film, and one can almost hear them plotting out this novel as a lark. A film critic and gossip columnist named Nigel Whitty is strangled with his own typewriter ribbon at a screening. In the locked screening room with him were assorted showbiz types, including a couple of second-rate critics, an internationally known female television interviewer, a Polish dancer who has defected and turned movie star, even a vegetarian poetess. All of the 11 people in the room had ample reason to kill Nigel, and all are delighted to see him dead. The likable young Irish cop on the case is assisted by the perky female columnist who had been Nigel's assistant. The cop's mother is a movie buff from way back, and likes to catch the old ones on afternoon television with a genial Irish priest.

This is a mystery, in short, that mocks not only the movie world but even the old movie mysteries. It is also a guided tour of Manhattan, from Lincoln Center to Studio 54 to the Cloisters to a penthouse on Central Park West, and ends with a chase through--you guessed it--Radio City Music Hall. Even to a non-New Yorker, several characters bear tantalizing ressemblances to real people, and the writers remember, like movie writers of old, to add some romantic interest.

What Nigel Knew is at least as much interested in its backgrounds as in its story line, particularly during the action scenes, which are unconvincing. The chatty writing of this novel skips over the story like a stone over a pond, but perhaps, as in the world it describes, the surface is the substance. In any case, it is not meant as a serious work but as a light entertainment, a mystery novel for movie buffs, a pleasant Sunday matinee.