Oh my, there are several proverbs that come to mind, however ..... 

Let this stand instead

"Colluding | Define Colluding at Dictionary.com
www.dictionary.com/browse/colluding
verb (used without object), colluded, colluding. 1. to act together through a secret understanding, especially with evil or harmful intent. 2. to conspire in a fraud.

Pretty concise definition, isn't it! Fits the situation to a T.