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Things are becoming more complicated or interesting. The police assumed that the woman was murdered by her ex-husband, but he has an alibi. The plot thickens. John is supposed to be going out with Mary, but I saw him last night with Sally. The plot thickens.
thicken something up
1. to make something, such as a fluid, thicker. I have to thicken this gravy up before we can serve dinner. Please thicken up the gravy before you serve it.
2. to make something wider. See this line here? You need to thicken it up so that it shows more clearly. Try to thicken up the line a little.
the plot thickens
something has become more complicated or interesting The plot thickens as police investigate dozens of deaths at a California hospital.
The plot thickens.(humorous)
something that you say when something happens which makes a strange situation even more difficult to understand I had assumed the Irishman who keeps phoning June was her husband, but it seems her husband is American. The plot thickens.See lose the plot
plot thickens, the
Circumstances are becoming very complex or mysterious. Today this term is often used ironically or half-humorously, as in His companion wasn't his wife or his partner-the plot thickens. Originally (1671) it 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.
See also: plot
1. To become thicker or denser: The gravy thickened up.
2. To cause something to become thicker or denser: I thickened the batter up by adding more flour. The cook thickened up the fudge.