“Someone keeps adding soil to my allotment The plot thickens…”

“The plot thickens” usually refers to a story or situation, but there is a pun:
 
“Someone keeps adding soil to my allotment overnight. It’s an absolute mystery as to why though. The plot thickens…”
 
The joke was cited on Twitter on March 10, 2010 and probably originated on Sickipedia.
 
   
Sickipedia
10 March 2010
Someone keeps adding soil to my allotment overnight. It’s an absolute mystery as to why though.
The plot thickens…
 
Twitter
Taz kingston
‏@thedjtaz
Someone keeps adding soil to my allotment overnight. It’s an absolute mystery as to why though?
The plot thickens…
4:33 AM - 10 Mar 2010
   
Twitter
Designergarten.at
‏@designergarten
RT @tonystamp Somehow..soil keeps being added to my garden overnight and I can’t work out how…....The plot thickens
5:27 AM - 10 Mar 2010
     
Fortean Times
Humour and Jokes
Yithian
Mar 11, 2010
From my father [prepare to groan]:
 
Someone keeps adding soil to my allotment overnight.
It’s an absolute mystery as to why though?
 
The plot thickens…
Yithian, Mar 11, 2010
         
Digital Spy Forums
sickipedia - a bit too far?
sbugg
18-03-2010, 11:31
(...)
Quote:
Someone keeps adding soil to my allotment overnight. It’s an absolute mystery as to why though.
 
The plot thickens…
 
Google Books
The Mammoth Book of One-Liners
By Geoff Tibballs
London: Constable & Robinson Ltd
2012
Pg. ?:
For the third night in a row, someone has been mysteriously adding soil to my vegetable patch. The plot thickens . . .
 
Twitter
LaffGaff
‏@LaffGaff
Someone keeps adding soil to my garden.
The plot thickens.
http://buff.ly/29uIqgj
#funny #jokes #jokeoftheday
4:12 PM - 12 Jul 2016