Henry finds the dead body of a beautiful woman in the woods while out bird watching. Even though Henry is technically retired from police work, he becomes invested in the case. However, when Shawn, Gus and the SBPD get involved, Henry's presence on the case is less than welcome. Since retirement, Henry has been seen as a guy too far removed from the game to be an actual player.
The dead woman, Shelly Aaronson, who they learn was very wealthy, looks like she could be in her 30s, but during her autopsy Woody discovers that she is actually 48 years old and that she had a ton of cosmetic surgery done. Shawn figures out that the cause of death was a reaction to a specific strain of Botox she had injected. Woody believes that this type of pristine work could only be Dr. Joan Diamond's work, Santa Barbara's premier cosmetic surgery doctor.
This clue leads Shawn and Gus to Diamond Surgical Group - a sleek plastic surgery business owned by Dr. Joan Diamond, the surgeon they believe Shelly got work done from. There, they learn that Shelly had sued Dr. Diamond before she was killed, but Dr. Diamond doesn't answer any of their questions. Much to Shawn and Gus's surprise, Henry shows up at the office to investigate and offer up his assistance on the case. Henry and Shawn immediately butt heads. They have competing theories as to what actually happened, so they split up to see who can solve the case first.
Shawn and Gus go to question Shelly's husband, Brad Turner, a physical trainer at a nutritional wellness facility called Thrive. They are immediately suspicious of Brad because he is much younger than his very wealthy, much older late wife. But Brad is clean because he signed a prenuptial agreement. Brad then gives them info that leads them elsewhere - to the coffee shop Shelly met a woman at the day she was murdered.
At the coffee shop, Shawn asks to see footage from their security camera. On the tape they see Shelly engaged in an argument with a woman whose face we do not fully see. Shawn gets a peek at the woman's nose and realizes it is the same nose he saw in a file at Dr. Diamond's office belonging to a woman named Briana Hicks. Shawn presents the theory that Briana killed Shelly after she realized Shelly had basically stolen the look of her face. Shawn and Gus approach Briana, but are surprised to see Lassiter already there, taking her away in cuffs. Lassiter tells them that Dr. Diamond hired Henry to solve the case and that all the clues Henry had found led him to Briana. Shawn is shocked to hear that his dad might have solved the case before he did.
Briana admits to being upset with Shelly for stealing her look, but says she did not kill her. She has an alibi and it checks out. Both Shawn and Henry were wrong about Briana. This causes Henry and Shawn to bicker about who is better at solving cases. And with that, the competition to solve the case first is officially on.
Shawn calls Joan Diamond pretending to be Henry. He gets an address from her - an address Shawn knew his dad was heading to later that day. The guys arrive at the address and realize they are at a Botox Party hosted by a plastic surgeon named Dr. Ted Lomax.
Henry arrives and is surprised to see Shawn and Gus. He tells them that Joan found out Shelly had been going to a different plastic surgeon, Dr. Ted Lomax, whom she believes to be a suspect. Shawn isn't so sure. Shawn sees a woman he recognizes at the party. He approaches her and realizes she's an employee who is leaving Dr. Ted to go work for Dr. Diamond. Her name is Leecy. Shawn questions Leecy and, from her testimony, he determines that it was Dr. Joan that killed Shelly. But Henry presents a solid case against Ted Lomax - that he isn't a real doctor and Shelly's death was accidental due to malpractice. Based on this theory, Lassiter and Juliet arrest Dr. Ted.
Joan thanks Henry for clearing her name by agreeing to a dinner date at Henry's place. But Henry is shocked when he finds a handful of Botox vials in Joan's purse - the same strain of Botox that ultimately killed Shelly. From this, Henry determines that he was wrong about Joan, but before he can make the call for her arrest she tells him the vials aren't hers and knocks him unconscious.
After Henry comes to, Shawn gloats about being right about Joan all along. However, Shawn checks out the fingerprints taken from the syringe and determines that Joan wasn't the one who injected the lethal dose of Botox into Shelly; if it were Joan that did it, there would be a thumbprint on the syringe and not an index finger print. A professional doctor would never inject fluid via syringe with their index finger. From this, Shawn comes up with a new theory - that the real killer was framing Joan and the only reason she knocked Henry out was because she panicked. Henry was right about her all along. Shawn and Gus then try to convince Henry that they need his help finding the real killer trying to frame Joan.
The three follow a lead to Thrive where they are shocked to find Brad dead. Woody confirms that Brad's death was not an accident. Back at the SBPD they then learn that Brad was from North Dakota and that he had an arrest record there. Shawn immediately remembers Leecy saying she was from North Dakota as well. And as it turns out, she has an arrest record in North Dakota too - Brad and Leecy were both arrested for fraud. It turns out Leecy and Brad are a couple who pull cons together. They hatched a plan for Brad to marry a rich woman and steal her money. But what they didn't plan for was Brad actually falling in love with Shelly. When Brad backed out of the con against Shelly and left Leecy out to dry, Leecy killed Shelly in a jealous rage. And when she found out Shelly was suing Dr. Joan, Leecy framed her for Shelly's murder. Leecy was the killer all along.
They rush over to Dr. Diamond's practice to find Leecy. Shawn and Henry do a special father/son breakdown of the case, each taking turns highlighting what really happened. They arrest Leecy and save Joan.
In the end, Henry and Joan have their second date, Shawn and Juliet are officially back together and Gus fears that his girlfriend Rachael, who has been in London for months, might break up with him.
- An amalgam of the 'Nip/Tuck' reference to plastic surgery, and the FX channel show of the same name, and the heroes' refrain of "Suck it!" (which may in turn be associated with Shawn's professional wrestling interest, and the WWE faction known as 'D-X'), the title in its composite form also suggests liposuction.
- According to the After Pshow, "Suck it!" was James Roday's favorite catchphrase from the show.
- This is essentially the last we hear of Rachael and Max.
The gallery for Nip and Suck It can be found here.