Charlie must make a difficult decision about his future and with which woman he wants to spend his life: Chelsea or Mia.
Girls rule the roost after Charlie consents to Chelsea's desire to allow Alan's girlfriend, Melissa, to move in with them.
Alan cares for Judith's child and his ex-mother-in-law. A photo Charlie would rather be kept private provides Jake with a chance to blackmail him.
Alan starts working for Evelyn as Charlie works to fix the relationship between Chelsea and Jake.
After being embarrassed in public, Jake stops at nothing to get away from Charlie and Alan.
Alan's advice to Chelsea that she get breast-reduction surgery is not met with enthusiasm by Charlie.
Charlie and Alan awaken to find themselves in bed with a stranger.
While overcoming a bad break-up, Chelsea invites her beautiful college roommate to stay at the house.
While Alan struggles to cure his baldness, Charlie deals with the problem that he can't satisfy Chelsea.
Charlie uncovers the truth that Chelsea has been lying about her finances.
Jake is taught the art of infidelity by Charlie, whose girlfriend is away for Christmas.
In order to woo his ex-girlfriend, Jake begins writing love songs, while Herb and Alan attempt to hide their secret friendship from the watchful eye of Judith.
Charlie opts to have a colonoscopy in order to avoid going on a trip with Chelsea to see her parents. However, when he returns home, he finds her parents at his house.
Strange things occurs when Alan winds up in jail because of a bar fight, and Charlie begins to worry that Chelsea might be "too interested" in the lawyer who takes the case.
Chelsea and Charlie's relationship may be destroyed by Charlie's jealousy.
Charlie runs off to Vegas and returns with a new wife, but she's not Chelsea.
Charlie and Chelsea have a post-breakup one-night stand.
Charlie has a return engagement with Chelsea's best friend, while Alan has an unexpected effect on a new female patient.
Alan is torn between the bad influence of Jake's new friend and the hotness of his mother.
Alan plans an intimate night at a hotel with Lyndsay, while Charlie tries another tack at getting a "girlfriend experience".
Charlie is haunted by ex-girlfriends while Alan and Jake are taking a road trip.
Charlie is miffed over Alan's planned attendance of Chelsea's birthday party and suffers the indignity of having Jake chauffer him around following a license suspension.