It took some ten years for Hollywood moguls to put the pieces together. The result was Harper, a decent detective yarn with a stellar supporting cast and a yummy pin-up girl (Pamela Tiffin).
What separates Harper from the usual genre entry is that Harper couldn't care less about Tiffin. Instead, he wants to get back together with his wife (Janet Leigh), who is divorcing him because he's never home. Instead, he's too busy proving that everyone is guilty, aside from his embittered client (Lauren Bacall).
Along the way, Newman encounters a sycophantic playboy (Robert Wagner), a drug-addicted blues singer (Julie Harris), an alcoholic washed-up actress (Shelley Winters), and various bad guys who (in detective story fashion) always prefer to beat Newman up rather than kill him.
Based on a Ross Macdonald novel, Harper has undercurrents unusual for a private eye movie. Culture was rapidly changing in 1966, with thirty-somethings feeling threatened by (and thus scornful of) rock music, religious peacenics, homosexuals, impoverished immigrants, and the younger generation in general. All must be put in their place by Harper, along with the pieces of the mystery.
As usual for the genre, the plot becomes more improbable as it moves along. Forgive me for divulging, but Newman is actually annoyed in the final frame that he hasn't been shot dead. And this is supposed to be funny!
But audiences were appreciative of Harper, and its multi-demographic pull made it a box office winner. The Edgar Allan Poe society was also impressed, as it won their award for Best Motion Picture.
Newman returned to the role of Harper nearly a decade later, in the sequel The Drowning Pool. The director of Harper, Jack Smight, later made another detective story; a scene-for-scene made-for-television remake of Billy Wilder's Double Indemnity. It was awful.