This was Episode 13, entitled 'Oona Wentworth.' Interesting observation, all of the official episode names are names of characters in the show, mostly women.
When Sean and Christian discover that Merrill Bobbolit (Joey Slotnick) is performing destructive cosmetic surgeries in an illegal backroom operation, Christian is motivated to help him recover his dignity. Ava (Famke Janssen) convinces Christian to perform surgery on an aging high school principal as a bribe to keep Adrian and Matt from being suspended from school.
Other bits from this show. Adrian and Matt get in trouble twice. The second time, Sean steps in with a dictatorial swagger to try and get Matt's life back on track. Taking a cue, Ava attempts the same with her son, Adrian. Throughout this entire episode, Adrian continues to be a thorn in everyone's side. Right up until the end. You see him sitting in a dark room, on a couch. Ava enters, asking him what's wrong, explaining to him why she's trying to help him even though it's not apparent to him, and that things can't go back to the way they used to be. Time for the bombshell. Ava ends up locking lips with Adrian (HER SON). Not only is she a pedophile but she's into incest as well. Crazy.
Next episode looks interesting. Apparently Dr. Troy sleeps with Kimber ("it's just sex" she proclaims). This is a two-fold problem since Kimber has been seeing Dr. McNamara and Dr. Troy has been seeing that blind woman (Rebecca Gayheart). Plus the true nature of Ava and Adrian's "relationship" comes out. All in all, should be another exciting installment!
Btw, I'd apologize for the synopsis (since I once said I wouldn't be writing about Nip/Tuck) except none of my law school friends watch the show. So where else do I get to minorly rant on it?