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Charlie bumps into Mia at the coffee shop and she asks Charlie to help her out with some music she has been working on. Charlie initially declines, but then Chelsea says that if he has no feelings for Mia, then he should have no problem helping her out. Concerned about what Chelsea said, Charlie visits Dr. Freeman, who says he must pick the woman he loves most. While working together, Mia makes a move on Charlie - who then tells her he loves Chelsea and leaves Mia for good. Meanwhile, Alan and Melissa officially reunite, and Charlie gets concerned wondering if Melissa has moved in. Eddie Van Halen has a cameo appearance.

When Chelsea convinces Charlie to let Melissa, Alan’s girlfriend, move in, the girls take over the house. Charlie angrily leaves the house to stay at a hotel after Alan and Melissa throw a party without asking him; Alan then gets himself kicked out by trying to stand up to Melissa and Chelsea. Alan and Charlie get Evelyn to tell Chelsea that Charlie had previously slept with Melissa - causing the two girls to have a falling out thus giving Charlie and Alan the house back.

Alan plays nursemaid to Judith’s baby and her tipsy mother Lenore (Annie Potts) while Judith and Herb try take a "romantic" getaway. Meanwhile, Charlie runs over a cat which he believes to be Chelsea’s cat, Sir Lancelot, and Jake takes a photo of the scene to blackmail Charlie in letting him drive his Mercedes. The two later find out that Chelsea’s cat is with her all the time, much to the relief to Charlie, but suddenly, a large muscular man comes looking for his cat - the same that Charlie ran over, to Jake’s delight of managing to blackmail Charlie again.

Sick of not having a place of his own to have sex with Melissa after a failed attempt of having sex with her in his Volvo, Alan takes a job working for Evelyn and invites Melissa over to a house he and Evelyn are selling and tells Melissa that he is renting it, but this backfires when Evelyn walks in on them, causing Melissa to leave and Alan to flee in his underwear which leads to his arrest. Meanwhile, Charlie is fed up with Jake’s bad attitude toward Chelsea and forces them to work out their issues alone in hopes that they will bond, but it turns out that it is Charlie’s fault that they are not getting along.

While Jake has been learning to drive, Charlie and Alan have been bickering nonstop. When this embarrasses Jake in front of a group of girls he likes, he refuses to stay with them anymore, and they have to find a way to convince him to continue spending weekends at the beach house. After their attempt fails, Judith snaps and shouts at Jake until he goes with them. In an attempt to resolve his antagonism with Charlie, Alan brings out an old relationship-counselling book he used with Judith, but he and Charlie use it when they are getting plastered.

Chelsea has been dealing with back pain, and Alan suggests she alleviate the pain with breast reduction surgery. Charlie learns of this and angrily kicks Alan out, and Alan is forced to temporarily move in with Evelyn; meanwhile, Charlie doesn’t want Chelsea to go through with the surgery, taking a big liking to her big breasts. Eventually, he comes to terms with it, but makes a remark about Chelsea’s body that puts her off the idea of surgery. Meanwhile, Evelyn scares Alan away by pampering him by buying him expensive clothes, and then asks him to cater her "needs" when she is old and crippled.

Evelyn announces that she will take care of Charlie and Chelsea’s wedding as a gift, and they finally have a set date; June 26 at the Bel-Air Hotel. Later that night, Charlie and Alan go out drinking and meet a woman (Katy Mixon), and they later wake up all in the same bed, but they can’t remember what happened; Charlie doesn’t know whether or not to tell Chelsea until Evelyn’s advice settles his conscience, but Chelsea is suspicious. Jake and Chelsea have a conversation about Charlie’s past flings, which makes Chelsea extremely uncomfortable.

Chelsea invites her beautiful college roommate, Gail (Tricia Helfer), to stay at the house while Gail gets over a bad breakup with her boyfriend, Brian. Charlie is struggling to resist his temptations toward Gail and wonders if Chelsea, who has a problem with him not listening to her, is testing him to see if he is going to hit on Gail. Meanwhile, Berta suggests he use Alan’s romantic ineptitude towards Gail to solve the problem which proves effective and successful.

Charlie is upset when he finds out he hasn’t been sexually satisfying Chelsea, and contemplates the reasons and tries to solve the problem. It is later revealed that Chelsea has found out that her ex-husband is getting remarried which has somehow negatively affected her sex life. Meanwhile, Alan tries to fix his oncoming baldness with a cheap hair product, called Captain Terry’s Spray-On Hair and pills that he bought online, which proves to be a disaster.

Charlie and Chelsea get into an argument about dancing at the wedding, and the two end up going to dance lessons together, where Charlie finds out Chelsea has been keeping secrets about her finances: she owns multiple properties that she had never mentioned before, making her richer than Charlie, which angers Charlie as she hasn’t paid any bills in the house while they have been living together. Eventually, she apologizes and they make up. Alan and Jake watch Alan’s old wedding video.

With Celeste (Tinashe), Jake’s girlfriend, away for Christmas, Charlie tells Jake that it’s okay to cheat on her with a girl he meets on the beach, but this backfires when Celeste returns unexpectedly as Jake arrives with the girl, which also lands Charlie in hot water with Chelsea. Meanwhile, Evelyn brings ailing TV personality Marty Pepper (Carl Reiner) to Charlie’s Christmas gathering, because she hopes to handle the sale of his $6-million mansion when he dies. At the dinner table, everyone trash-talks Charlie after the cheating incident.

Jake is still angry with Charlie about the incident with Celeste, and he decides to sing her the love song he has written in an attempt to win her back. Charlie suggests that instead he try apologizing in person, but when that fails he says Jake will soon find another girl, and although he is doubtful he soon does. Meanwhile, Alan and Herb begin to bond after going out to eat together, but Judith will not let them spend anymore time together.

Charlie schedules a colonoscopy to get out of visiting Chelsea’s parents, Tom and Martha, in Illinois, but Chelsea figures out he was lying and flies them into Los Angeles instead. During a night drinking with Chelsea’s father (Stacy Keach), Charlie and Alan learn that he is homosexual and in love with an African-American war-buddy of his, which is also in contrast with Martha’s beliefs since she is an extremist and racist homophobic. Chelsea then overhears her mother and father arguing about the situation; the two then break up.

Alan ends up in jail after a bar fight and Charlie worries that Chelsea might be interested in Alans’ lawyer, Brad Harlow (Steven Eckholdt), who takes the case, because he claims to be a family man, and horse range charity-founder. Brad invites Chelsea and Charlie to his charity event, but Charlie decides not to go, leaving him to wonder if Chelsea is actually cheating on him with Brad.

Charlie becomes worried and jealous after Chelsea is late returning from a charity event with Brad. When Chelsea does return, she and Charlie argue and Chelsea leaves, and Charlie drowns his sorrows repeatedly. Chelsea later asks Charlie to meet her for coffee; during this meeting, Charlie throws up on a woman’s baby, leaving Chelsea to postpone the wedding and breaks up with Charlie. Evelyn comforts Charlie, but adds that most people throw up on their own babies, rather than other peoples.

After Chelsea breaks up with him, a depressed Charlie takes a trip to Las Vegas and returns home with a new wife, Betsy. Charlie then finds out that his new "wife" is already married, and her husband says that she regularly has affairs, which he tolerates because he’d rather share her than not have her at all. Charlie then spends some time with Chelsea’s father, Tom, and his new boyfriend, Ed. John Amos guest stars as Ed. Katy Mixon guest stars as Betsy, who could be the same character (also played by Mixon) who appears in "Untainted by Filth", but neither Charlie nor Alan recognize her!

Chelsea has started dating Brad. Charlie stalks her with the help of Alan, and after having a post-breakup one-night stand, the two are left re-thinking about if it was right for them to break up. Charlie tries to win her back, and takes relationship advice from her father and his boyfriend; Charlie tells Alan he likes having him live at the house which brings Alan to tears of happiness.

Charlie runs into Chelsea’s friend Gail (Tricia Helfer) at the Pizza shoppe for Jake’s new haircut, which he got because of his new girlfriend. He has sex with her, but then learns that Chelsea is having problems with Brad. Charlie later meets Chelsea for coffee and tells her that he slept with Gail, causing Chelsea to angrily storm off. She later comes round his house to apologize but again storms off after thinking that Gail is still there in Charlie’s bedroom. Meanwhile, Alan finds himself able to pleasure a female patient just by giving her a back massage but worries he’s becoming a sort of gigolo due to the large amounts of cash that the woman is paying him.

Jake’s new friend, Eldridge (Graham Patrick Martin), proves to be a bad influence when he talks Jake into stealing beer from Charlie, getting drunk and sneaking out when grounded. Charlie catches Jake sneaking out, but lets him off the hook after Jake and his friends felicitate Charlie on the current jingle he’d written. Alan plans to have words with Eldridge’s mother, Lyndsey (Courtney Thorne-Smith), but ends up falling for her and the two later make the most of a trip to a bar.

After being interrupted at Lyndsey’s house by her son, Eldridge, Alan tries for an intimate night at a hotel with her, but nothing goes as planned due to the fact Lyndsey suffers a bad period, and Alan gets an upset stomach. Meanwhile, Charlie tries to get the "girlfriend experience" from a prostitute, Jasmine (Elizabeth Ho), by having her and himself act as a real couple with real problems. The prostitute actually takes a liking to the role.

Charlie finds himself with insomnia, and is given prescription marijuana by his pharmacist (Martin Mull) to help him sleep. After smoking it with Berta, Charlie has disturbing visions of women from his past; Alan and Jake have a road trip to Sacramento to pick up a valuable antique grandfather clock left to Alan by Judith’s recently deceased grandfather. While riding home in the car, the clock falls out of Alan’s trunk and smashes in to pieces, making his and Jake’s trip futile. ZZ Top guest star as themselves.

Jake is driving Charlie around when he runs a red light at Charlie’s urging, and is pulled over by police, causing Jake to panic. He and Charlie switch seats so that it appears Charlie was driving, and as a result, Charlie loses his license due to several unpaid traffic violations and failure to show up in court, forcing him to rely on Jake to drive him around. Alan goes to Chelsea’s birthday party, and Charlie sends Jake in too so that he can give her a forgotten gift. After being given the gift Chelsea leaves in an emotional fit, only to find Charlie being arrested for crashing into a police cruiser.