After her interview with Tim Gunn is sabotaged, Jenny reveals a secret that will damage everyone involved.
Meanwhile, Serena learns that Colin is actually her college professor, which puts their relationship in grave danger.
Vanessa then becomes collateral damage in Juliet's vendetta against Serena when she frames her for causing trouble in Serena's academic career.
Elsewhere, Chuck threatens Blair's chances to become the powerful businesswoman Martha's new assistant.
Title reference: From the 1967 film, Belle de jour.
The series was developed for television by Josh Schwartz and Stephanie Savage.
However, Serena and Blair find a way to expose Juliet's sabotaging plans. Chuck is afraid of introducing Eva to Lily and Rufus, since she doesn't know of his past indiscretions.
Title reference: From the 1995 film, The Underneath.
Vanessa joins Juliet's scheme to try to bring down Serena when damaging information about Serena falls into her lap.
Nate discovers Juliet's real secret and Dan realizes that he still has feelings for Serena.
Title reference: From the 1987 film, The Witches of Eastwick.