"The Veiled Lady" is a very intriguing Hercule Poirot mystery from 1990.
A beautiful young woman asks Poirot to retrieve letters for which she is being blackmailed. The blackmailer comes to Poirot's office by invitation. Poirot attempts to negotiate with him, but the man only comes down a few thousand pounds. It's futile. He mentions that he will contact Poirot when he returns from Paris. Poirot decides to burgle his house and find the letters.
Wearing a cap, he presents himself to the housekeeper as an electrician and proceeds to begin searching. The housekeeper is very uppity and talks his ear off, stating that she is not live-in. Poirot leaves, informing her he will be back tomorrow.
That night, he and Hastings break into the house. Poirot finds the letters in a Chinese box inserted in a log. Turns out, the housekeeper was lying -- she says she knew he was casing the joint -- Hastings panics and takes off, throwing himself out a closed window. It was hilarious. Poirot spends the night in the slammer, Japp pointing out to a junior office that this particular prisoner is especially dangerous and called "Mad Dog."
It unfolds from there. It has a neat twist and it's filled with humor. Loved the ending. One of the livelier episodes. Poirot is finally released