The BLU Heavy gets a copy of Left 4 Dead 2, and is extremely excitable as he barges into his room and puts the CD in his computer. The game asks for a serial key, light heartedly threatening to eat Heavy if it's invalid. but with his oversized fingers Heavy accidentally presses several keys at once while typing. Possibly because of getting it wrong, Left 4 Dead's Francis bursts out of the computer monitor, then drags Heavy inside and into the computer's world, which resembles an enormous house. The confused Heavy finds himself standing next to Left 4 Dead 2 character Ellis, who introduces himself. Heavy seems to take an instant dislike to Ellis, crushing his fingers in a handshake and throwing an offered pistol at his face. Ellis merely responds by giving Heavy a teddy bear.
Meanwhile, the shifty Chuck Greene and more childlike Frank West, both from the Dead Rising games, meet each other atop a huge desk. West pesters Greene in order to get Greene's gun, when a zombielike Scout attacks the two. West randomly decides to shoot Greene before shooting the Scout, and Greene retaliates by setting out a table, and kicks up a cloud of smoke as he creates...an entire machine gun turret, out of seemingly nowhere. He opens fire on West, but runs out of ammo, during which time West runs over to the turret and completely disassembles it. West simply smiles at Greene's annoyance.
Back with Heavy, Ellis decides to show him his dance moves, and also shoot an injured Coach, much to Heavy's bemusement. They're interrupted by a horde of wild animals, and while Heavy is swept away by a flock of birds (and the G-man) Ellis tries in vain to shoo the turtles away. Ellis is knocked off the edge, but lands on the back of a rocket powered horse. Heavy is whisked into the lamp on the ceiling of the room, and corned by a group of turtles. Ellis flies in on the horse to rescue Heavy, who ends up falling, and falling, and falling, and remixed falling to the ground beside the giant bed. Ellis falls down the front of the giant dresser, and hits every possible object on the way down. Both end up on the ground, calling out for help.
At the table of Greene and West, West advises Greene to dye his shoes blue and cream, but Greene merely gets fed up and throws him into a refrigerator. After a few moments, Greene gets suspicious, then reopens the fridge to find it empty. All of a sudden, Francis appears behind Greene and executes a Monster Kill. He then promptly leaves on a bumper car, high fiving West on the way past. An annoyed Green smacks West.
Ellis and Heavy finally start to quieten down, when all of a sudden Ellis claims to hear a Smoker, namely a belligerent Bill from Left 4 Dead. Bill viciously attack the two, when Ellis grabs a container of Viagra pills and downs them. As a result, his testicles swell to an enormous size, and he begins imitating Duke Nukem as he knocks the Smoker-Bill and Heavy away. Ellis speedily kicks the asses of a zombie group and a Heavy/Panda hybrid. The testicles have returned to normal the next time we see Ellis.
In a large room, Greene and West encounter a man hunched over on the ground like a Witch. West, who is carrying a coffee mug, is in disbelief. The man suddenly notices the zombie hunters and screams for someone called Jason as he lurches over. Before he can get to the two, a car bursts in spectacularly and knocks them all down. An affable yet rough handed FBI agent gets out and arrests West. He takes West back to the 'interurgashun rewm', where West says nothing, but just coyly offers him and another agent some of his coffee. The second agent knocks West to the ground in a fit of rage, then does the same to his partner when he protests. Suddenly, Greene, who had been left behind, literally explodes into the room, and West and Greene perform a daring escape to the tune of 'America (Fuck Yeah)'.
In a room that seems to be a mouse hole in the wall, Heavy catches a scent. He peeks out to see two procrastinating, yet aggressive and seemingly adolescent, guards wearing armour from Gears of War, and a Crit Sandvich on the table. Heavy immediately begins studying a book on how to sneak past guards, while Ellis flies across the room (Twice. The first time he crashes into the cameraman by accident.) An affectionate Half Life civilian appears, and seems to mistake Heavy for Gordon Freeman (probably because of Heavy's reading glasses). Ellis has an idea, and produces a box with a costume for the civilian inside. The civilian refuses point blank, but is 'persuaded' by Heavy. The reluctant civilian is shoved out in a Renamon costume, and the guards react with immediate loathing. They attack and defile the false Renamon, while Heavy sneaks off with the Crit Sandvich. Heavy manages to find somewhere to eat the sandvich in peace, while Ellis follows him. Suddenly, Ellis is stabbed through the throat and seemingly killed by an overdramatic Ezio from Assasin's Creed. The assasin attacks Heavy with a flurry of knives, but thanks to the sandvich, Heavy is indestructible, and promptly and brutally disposes of Ezio. Heavy spares a couple of seconds mourning Ellis, then happily rushes off.
After a small intermission involving a strange and slang ridden conversation between two gangsters, the story has probably the briefest recap ever made and then cuts back to the action. Heavy is looking about through binoculars at various scenes, as if on a top secret mission, when suddenly Ellis appears in front of him. Heavy is angry and annoyed at Ellis, but is suddenly revealed to be upside down and plummets. A convenient giant trampoline launches Heavy back up, where he holds onto a ledge by his fingers. Dramatic tension builds as Ellis slowly reaches for Heavy, while Heavy slowly loses his grip, then Ellis is distracted by a christmas tree and Heavy just yanks Ellis down with him as he falls. Coincidently, they fall onto a car driven by Greene and West in their escape, and the parties meet up. The road is suddenly blocked, and something huge, shadowy and terrible rises up in front of them...and it's a giant cat. The adorable 'awww's are short lived when the cat reveals it has disintegrator eyebeams. The heroes flee in terror from the massive flying cat, but there seems to be nowhere to run as the cat disintegrates them one by one. Greene retaliates by setting stuff on a table, and kicks up a cloud of smoke as he creates...a toaster, which he can't enjoy before getting vaporised. Soon just Heavy is left, and he flees along a train getting blasted behind him by the terrifying cat. Suddenly, Heavy decides to stand and fight. He jumps in front of the train and PUNCHES it right at the cat. He picks up a bit of glass and uses it to hold off the eyebeams just long enough to reach for a bottle of water, and throw it at the cat. The cat is knocked down, and beats a hasty retreat. The Heavy gives a triumphant cry, and all his allies celebrate his survival.
Heavy suddenly wakes up at his desk. He looks outside, and is amazed to find it is snowing. He looks around for the rest of BLU Team, but seems to be alone. One 'trip' downstairs later, he finds the whole team in the front room celebrating Christmas. The Scout tosses him a copy of Left 4 Dead 2, which the angered Heavy promptly throws right back. There is a sudden ring of the doorbell, Heavy answers it, and who should be there but Ellis. Heavy slams the door on him, but not before Ellis can put a present through. Heavy opens it up, to the tune of Zelda chest-opening music, and discovers the very same teddy bear Ellis gave when they first met. Moved to tears, Heavy lets Ellis in and gives him a massive hug. Ellis merely smiles at the audience as the film irises out and ends.