Oscar Madison reluctantly agrees to let Felix Unger, his uptight former college roommate, move in with him after both of their marriages fail.
When Oscar is hired to ghostwrite the autobiography of a retired baseball player, Felix offers his "help" by advising Murph to go in a different direction, making Oscar's job more difficult.
When Oscar realizes he's forgotten Felix's birthday, he pulls together a last-minute surprise party in his honor in an attempt to impress Casey.
When Dani reveals she's depressed that she'll be the only single one at her high school reunion, Oscar and Felix each put their distinctive dating strategies to work to help her find a boyfriend.
When Oscar and Felix attend the wedding of an old college friend, Oscar aims to reconnect with an old flame while Felix is determined to show his ex-wife that he's a changed man.
Felix's hypochondria kicks into overdrive when Oscar starts dating the most important person in Felix's life - his doctor.
Felix convinces Oscar to appear on a sports television show against Teddy's advice to stick with radio.
When Oscar feels threatened by Felix's surprising performance on the softball field and basketball court, they agree to a decathlon to determine which one of them is the better athlete.
When Oscar and Felix make a trip to Ashley's to retrieve Felix's special pillow, a secret that he has kept from Oscar is revealed.
When Felix substitute teaches a yoga class, his teaching style rubs everyone, including Emily, the wrong way. Also, Oscar and Dani get trapped on a subway car, adding to their frustration about living in the city, and Murph asks Teddy to be his agent when he's approached to be the spokesperson for a Norwegian health supplement.
Oscar becomes obsessed with living up to Murph's standards when he finds out the girl he is seeing used to date the handsome ex-baseball player. Also, when Emily volunteers to be a part of a historical reenactment on Ellis Island in order to spend more time with Felix, he is too busy preparing for his role to pay any attention to her.
When the IRS decides to audit Oscar and his ex-wife Gaby, Felix offers to mediate between the contentious exes when he realizes that he might be the reason Oscar was audited in the first place.