NOTE: This spoiler was sent in by Alli
The movie begins with one of many montage-like scenes. We see Brennan Hoff (Will Ferrell making homemade nachos and being lazy on the couch watching an 80’s work out video as his mother Nancy (Mary Steenburgen) leaves for a conference. After Nancy leaves Brennan proceeds to stick his hands down his pants to presumably masturbate to the video.
Cut to Dale Dooback (John C. Reilly) who is jamming out on Guitar Hero as his dad Robert (Richard Jenkins) also prepares to leave for a conference and tells Dale he left him 20 dollars for pizza, but not to buy anymore pay-per-view, to which Dale complains that 20 dollars is not enough to also get wings with his pizza.
Next we are at the conference, as Robert (who is a doctor) is giving a presentation on hearing aides he is suddenly smitten with one of the audience members, Nancy, the two lock eyes, and next thing you know they are in a hotel room passionately ripping off each others clothes as they introduce themselves to each other and both realize they have 40 year old sons who both still live at home. Next scene we are at Robert and Nancy’s wedding. Both Dale and Brennan are miserable sitting at opposite tables and both storm out of the wedding but not before Nancy proceeds to tell the whole audience Brennan still lives at home and was recently fired from Pet Smart.
Next scene we see Nancy and Brennan driving to Robert and Dale’s house to move in. Brennan is in the back seat and not to happy about the situation and tells Nancy that Dale better not get in his face. Just as a side note, throughout the entire movie both Dale and Brennan pretty much act like bratty adolescent boys who have very obscene language. Nancy and Brennan arrive to Roberts house and at first Brennan will not get out of the car. Eventually he does and him and Dale stare at each other from a distance and the title of the movie “Stepbrothers” appears between them.
Next we find ourselves at what appears to be the families first dinner together. We find out Brennan is apparently a great singer and Dale and him constantly throw rude but hilarious remarks at each other that leads to Brennan almost breaking out in tears. Robert tells Dale to show Brennan their room, which they will be sharing because Dale refuses to give up his “drum office” which is just a spare room with a drum set in it. On the way to their bedroom they stop to look at the drum set and Dale warms Brennan to never touch the drums.
Next scene we see Dale and Brennan laying in bed whispering more hilarious remarks about how much they hate each other. Cut to Robert and Nancy in their bed talking about their dream, to sail around the world in Robert’s sailboat. They also both discuss why their respective sons both still live at home. Robert says after Dale’s mother died he developed a sense of arrogant entitlement and just always mooched off his money and said he was going to take over the family business (which, Robert is a doctor in a hospital, so there is no family business). Nancy traces Brennan’s problems back to a talent show where he was singing and asked the choir to back him up. However, Dale’s younger bullying brother Derek (Adam Scott) replaced the choir with his football buddies and they all started singing “Brennan has a man-gina” to which the entire auditorium joined in, including even Nancy. And thus Brennan was scared for life. Derek went on to win that talent show by lip-synching “Ice Ice Baby.”
Next we come to another montage of Dale and Brennan trying to make each other miserable. Dale kicks Brennan off the boat while the family is out sailing and Brennan paints a huge gross looking open wound on the top of Dales head so when he walks around town people run in fear and disgust from him. Finally, one day, Brennan decides to play Dale’s drum set when he is not home. Dale returns, figures out Brennan played his drums and next thing you know we see Brennan pulling out his testicles and rubbing it all over the drum set (and yes, you actually see Will Ferrell’s testicles) and then the two begin a hilarious physical fight which takes them all the way outside. Nancy arrives home and frantically calls Robert to come help. In the front yard the neighbors have gathered, some with coffee cups, to watch the fight. Eventually both Dale and Brennan knock each other out at the same time and fall to the grass. Next scene we see both sitting on the couch with ice packs to their head while their parents are furious with them and tell them they need to get a job within a month or they will be kicked out and, as an additional punishment, no TV for a week to which both Dale and Brennan freak out. However, at this point we start to see the two are starting to bond a little.
The next day Brennan’s brother Derek comes for dinner. Derrick and his family are in a range rover on the way over and break into an A capella version of Sweet Child of Mine, which is pretty entertaining. We can tell right away Derrick is a giant a-hole and, to use the term used countless times throughout the movie, a total douche bag. We can also tell Derricks wife Alice (Kathryn Hahn) is not very happy with her life.
At dinner Derek is telling a story about hanging out with celebrities on fishing trip (he is the VP of an executive helicopter company) and Robert is smitten with Derek and does not even bat an eye when Derek openly makes fun of Dale after he tries to ask a question. Brennan is not at dinner and Dale goes to find him sitting in their giant tree house in the back yard. Dale agrees with Brennan that Derek is a horrible person and the two bond even further while looking through Dale’s collection of Hustler magazines from the 70’s, 80’s, and 90s (again, more great one liners and hilarious moments). Derek pops his head into the tree house and gives the two a hard time and finally, fed up, Dale punches him right in the face.
Derek and his family (which includes two kids) leave, but not before Derek, who also apparently has his real estate license, tells Robert to sell his house and go sail the world (to which Robert enthusiastically agrees and falls even more in love with Derek). As the family leaves Alice stops Dale, and in a hysterical yet awkward moment, thanks him for punching her husband and that she is super turned on by him and tries to make out with him before leaving.
Next we find Brennan and Dale in their bedroom becoming friends. Another montage of the two becoming best friends, doing karate in the garage, watching a movie together, and finally, making their beds into bunk beds (which, if you have seen the previews, does not work out well).
The next day the two go on interviews that Robert set up for them. They both wear full tuxedos and sneakers and go on the interviews as a “team” which, obviously does not go over well. They even have an interview with Seth Rogan to pretty much be part of his entourage, and almost get the job but after a long and gross fart from Dale, Seth tells them to leave.
On the walk home they talk about starting their own company using their respective skills as a drummer and singer. They don’t want to start a band, but instead an entertainment company, Prestige Enterprises. As they are walking they come to a road that Dale refuses to go down and wants to take an alternate yet much longer route home because of a bully that hangs out on this road. Brennan makes him go anyway and we find out the bully is only an adolescent boy with his schoolyard friends on a playground. However, the school kids proceed to beat up both Dale and Brennan and make them lick old dog poop that has turned white in the sun.
Cut to the next scene, Dale and Brennan are sitting on the couch with black eyes as Nancy tries to comfort them. Then we see Derek walk out of the kitchen with Robert the two laughing and we find out the house is going on the market and both Dale and Brennan are soon going to be out on their own. Their parents, not to leave them empty handed, are going to give them enough money for a down payment on an apartment and have set them both up with therapists.
The next scenes involve Dale and Brennan at their therapist’s offices. Brennan’s therapist is a fairly attractive woman who Brennan immediate expresses his love to and for the rest of the film calls her his girlfriend even though she constantly tells him no. We also see Derek’s attempts to show Roberts house to potential buyers and Dale and Brennan trying to do their best to thwart his efforts by such things as dressing up as a Nazi and Ku Klux Klan member and posing as neighbors.
Dale and Brennan decide they need investors for their company and decide to make a music video but Dale tells Brennan he needs to hear him sing to which we get a pretty funny rendition of a Bonnie Raitt song from Brennan, which Dale praises.
Next we are at a restaurant for Derek’s birthday. Alice surprises Dale in the bathroom and another awkward but funny moment as the two have sex and then she proceeds to pee standing up in the urinal. After all of that Dale and Brennan announce their company and show their music video which is a rap called “Boats and Ho’s” (pretty funny). The whole time Robert notices they are on his sailboat and ask who was driving the boat and at that moment we see the boat crash into some rocks.
On the ride home Robert is furious and pretty much looses it. Next cut to Christmas Eve, you can tell the family is not happy and Robert goes off to have a drink at the local Cheesecake Factory. He returns later that night and him and Nancy have a little fight and Dale and Brennan, who are both sleepwalkers (there is another sleepwalking scene earlier in the film with is great) decide in their sleeping state to begin to through around all the presents and even bring the Christmas tree into their parents bedroom. Robert can’t take it anymore and decides to wake the sleepwalking boys (even though Nancy begs him not to) and in their confusion after being woken up they throw Robert down the stairs.
The next day at dinner we learn that Nancy and Robert have decided to divorce and move out and Robert tells Dale and Brennan that it is completely their fault to which they begin crying. The next day Robert and Nancy move out and Dale and Brennan are left at the house with one day to figure out what to do. That night they go back to hating each other and have another fight which ends with Brennan burying Dale alive (he gets out of the grave) and they roll around fighting and eventually pass out on the lawn. They wake up and decide to go their separate ways.
Next we see the two trying to get jobs and be grown ups. Brennan goes to work for his brother and Dale gets a job as a caterer. Both get apartments and we even see Dale reading a Montell Williams motivational book and going to bed at 8:45pm. Things seems to be going alright for the two and Brennan even asks Derek if he can take on the task of organizing the Cantina Wine Mixer (a big party to gain new clients for the helicopter company) to which Dale says sure because when he messes up he’ll be able to fire him.
Cut to the Cantina Wine Mixer, which has turned out great. Brennan has even hired the catering company Dale works for and both Robert and Nancy are there. Everything seems to be going well. Horatio Sans heads the band hired for the party and they only sing 80’s Billy Joel songs. One of Derek’s a-hole friends keeps yelling out for them to play Billy Joel songs from other decades to which Horatio freaks out on him and a fight breaks out and the band leaves and Derek yells at Brennan and fires him for ruining the party.
Robert rushes over to Brennan and Dale and urges them to go up on the stage and start having fun again, he can’t stand seeing them so grown up and miserable. Dale goes up and starts playing the drums to which the audience starts booing and throwing food. Brennan eventually joins him and starts singing an opera song (and forgive me I do not know the songs name but it has been sung by both Andrea Bocelli and Josh Groban I believe). Brennan’s voice and rendition of the song is so apparently touching that the audience loves it, Robert and Nancy fall back in love, Derek remembers when him and Brennan were young and best friends, and both Alice and Brennan’s therapist (who is there) have short and funny fantasies about their respective men, Dale and Brennan.
The Cantina Wine Mixer is a success. Robert and Nancy are back together, Derek gives Brennan a half-apology and the two (kinda) hug and Dale tells Alice they can’t be together. Cut to a few months later the whole family is at dinner and this time Dale and Brennan are the center of attention and telling a story about their new successful karaoke business and even Brennan’s therapist/girlfriend is there. Robert and Nancy tell Dale and Brennan a surprise waits outside for them and when they go out they see Roberts old sailboat made into a new tree house for them. Dale and Brennan are overcome with joy and rush to the tree house followed by Derek and his two kids. In the tree house the two find more gifts including pirate hats, nudie magazines, and even Chewbacca masks. Everyone is laughing and happy. Brennan’s therapist tells Nancy and Robert that this is totally insane to which they agree and the movie ends.
A little after the credits roll there is a short scene where Dale and Brennan return to the playground in a helicopter and proceed, in a fairly funny scene, to beat up the kids who beat them up earlier in the film.