It usually refers to things becoming overly complex or mysterious. Today this term is often Played for Laughs. Coined in the 17th century, it originally described the plot of a play that was overly intricate, and by the late 1800s it was used for increasingly complex mysteries in detective stories.
The phrase is sometimes parodied as "The plot sickens". You may also hear "the plot thins" - usually uttered after a major Anti-Climax.
- In Face/Off, Castor Troy's response upon walking in on Jamie wearing just her panties and a cropped t-shirt.
C.S. Lewis: He comes; he sleeps; he goes. So the plot thickens.
- In Kill Bill, Bill proves himself to be a lover of tales. So of course he says this.
- Discussed in The Grand Budapest Hotel.
M. Gustave: The plot "thickens", as they say. Why, by the way? Is it a soup metaphor?
- Famously used in the Sherlock Holmes story A Study in Scarlet, as uttered by Holmes himself.
- One of the chapters in The Phoenix Guards by Steven Brust is titled "In Which The Plot, Behaving In Much The Same Manner As A Soup To Which Cornstarch Has Been Added, Begins, At Last, To Thicken."
- A chapter heading in Making Money refers to it, but is "the pot thickens". This makes sense in context because Moist believes temporarily that Gladys, his golem secretary, is cooking his dog in the pit she's stirring. It turns out to be the sheep's head Adora Belle ordered for dinner.
- One of the Enchanted Forest Chronicles books has a chapter titled "In Which The Plot Thickens", which is followed shortly thereafter by one titled "In Which The Plot Positively Curdles".
- Hawaii Five-O (1968) pilot episode.
Wo Fat: As we clever Chinese say, "The plot thickens..."
- Knight Rider episode "Mouth of the Snake"
Michael Knight: So, the plot thickens. I bet this guy David Dalton is not down in Mexico looking for the world's biggest burrito.
- The League of Gentlemen
Pauline: It's about Mickey. He's getting married.Ross: Oh-ho. The plot thickens.
- M*A*S*H: Inverted as Hawkeye, Henry, Trapper, Klinger and Radar are watching home movies of Frank's wedding.
Hawakeye: The plot thins.