"Peeper" is not a bad little film and it will fit the bill if you are looking for a time-passer. There are also parts of the film I really liked (such as the snappy dialog). But it's also a film that has problems. The plot seems derivative (very much like a reworking of "The Big Sleep"), the story is confusing and inconsistent and the actors seem to try their best with a plot that really seemed forced. Because of all this, I certainly will not heartily recommend it.
The film is set in the 1940s and is introduced by an actor pretending to be Humphrey Bogart. The story itself then begins. A nutty guy (Michael Constantine) gets a private eye (Michael Caine) to take a case. He wants Caine to locate his long-lost daughter, as he wants to make her his heir. The trail leads to the Prendergast family and one of their two daughters MIGHT be the heiress. To complicate things, two thugs are on his tail and seem ready to kill him--and yet, inexplicably, each time Caine captures them he gives them a chance to escape instead of either turning them into the cops or shooting them. This actually frustrated the heck out of me--and again and again, Caine's character seemed to make dumb decisions. I hate films where you must accept the stupidity of the lead in order to make the plot workable! It's a shame, as Natalie Wood is gorgeous and Caine tries his best. It's just the case of a film that needed a re-write before it was actually made.