* Agatha Christie takes a simplistic view of human nature. In The Mirror Crack'd the whole plot hinges on ideas like "he just wouldn't do that" and "it's just the kind of person she is." Judging from those I've read, her books must be approached as mere puzzles, not literature. But "The Mirror Crack'd" is an unusually clever puzzle -- all the clues are put before you, and if you're like me, Miss Marple will have the answer long before you do. The new film version is restful and domestic after such exotic outings as "Murder on the Orient Express" and "Death on the Nile." We're stuck in a quiet country town, with Angela Lansbury figuring out who killed the local gossip as she chatted with a movie star while Elizabeth Taylor traders barbs with Kim Novak. No excitement -- a lulling evening at the movies and not unpleasant. Gu y Hamilton was the director.