NOTE: This spoiler was sent in by Robert W.
The movie actually opens with four brief trailers. The first is for Alpa Chino (Brandon T. Jackson) advertising his energy drinks while singing a song about "pussy". Next up is Revolver VI, an action trailer starring Tugg Speedman (Ben Stiller) as he wields a couple of guns and carries some babies. The third is for Jeff Portnoy's (Jack Black) new comedy The Fatties, where he portrays a bunch of fat characters in lousy make-up that fart every chance they get. The final is for Kirk Lazarus' (Robert Downey Jr.) movie Satan's Alley, where he appears to be in a homosexual love affair with a fellow monk, played by Tobey Maguire. Following these movie trailers, the actual film starts.
Four Leaf Tayback (Nick Nolte) explains in a brief monologue about what's going on -- currently, they're shooting a movie based on his book Tropic Thunder. Three helicopters fly in with various soldiers in them, including characters played by Portnoy, Chino and Speedman. Also along for the ride is Kevin Sandusky (Jay Baruchel). They land the choppers in an attempt to rescue men on the ground, with several soldiers getting shot. Sandusky gets stabbed by a soldier, with his guts ripped out of his body. As he attempts to tuck it back in, the platoon members run back to the choppers. Lazarus' character tells the chopper to wait, as Tugg Speedman's character comes running in for rescue. He is shot several times, and Lazarus gets out to confront him. They have a brief moment of drama when Speedman is bothered that he can't cry like Lazarus. Meanwhile, Portnoy hangs off a chopper in the background.
It's then revealed that the whole thing is a film in production. Director Damien Cockburn (Steve Coogan) is frustrated with Speedman, but attempts to work with him. After two more failed takes, the actors and director have an argument. In the midst of this, the special effects guy, Cody (Danny McBride), thinks he has a signal to set off a gigantic pyro and does so, blowing up the set in a tremendous manner.
An Entertainment Tonight report (hosted by Maria Menounos) talks about the embarrassing on-set incident, and how it's a huge embarrassment to Speedman, who's still trying to get over a dramatic box-office bomb where he played a mentally retarded boy named Simple Jack. Speedman is watching the report on TV and gets on the phone with his agent, Rick Peck (Matthew McConaughey), who tells him everything is going to be alright. He asks if he got his TiVo hooked up yet, to which Speedman replies it isn't. Peck tells him to work on his drama and concludes the call.
Meanwhile, Cockburn and Tealeaf attend a meeting held by studio executive Rob Slolom (Bill Hader), who puts them into a video conference with another executive, Lee Grossman (Tom Cruise). Grossman demands a grip punch Cockburn, which he does. Grossman explains that the film has to be made, and doesn't care how it's done. Tealeaf makes a suggestion, but Grossman simply brushes it off.
Cockburn, incredibly frustrated, runs into Tealeaf later in the evening as he sits in a makeshift shed. He explains the best way for the movie to get made is to put them "in the shit", right in the middle of a real combat scenario with cameras rolling around them. Cockburn agrees.
The next day, the acting team, along with Cody, Tealeaf and Cockburn, board a chopper and fly into the middle of the Vietnam jungle. The acting team and Cockburn get out, and the other two take off for higher ground. Cockburn, developing an attitude, snags all of the crew's cell phones (except for one of Speedman's, which he hides in his pants), douses them with water and stomps on them. He then explains that the film is going to be made his way and gives instructions. Before they can get started, however, Cockburn steps on a land mine and explodes.
The actors think it's fake. Speedman even walks up and starts licking out of Cockburn's head to show it's fake, while the others get semi-sick. Meanwhile, in the distance, a real team of renegades hide in the bushes, guns at the ready. They see what Speedman and his team are doing and think they're fearless. They prepare for combat.
Meanwhile, Cody and Tealeaf don't hear from the team, so they decide to set off one of the bombs planted in the area (for realism effect). The renegades and actors get in a firefight, and Cody sets off the explosive just when Speedman throws a fake grenade. The renegades run away, and Speedman and his team decide to head off with the shooting schedule. Cody and Tealeaf, not hearing anything from Cockburn, decide to fly back to the drop point.
The actors make their way across the jungle. Lazarus begins to think that the whole mission is a wash, while Portnoy seems content with a bag full of his "jelly beans". Speedman keeps a close eye on the map. At one point, Sandusky stops to take a leak. Lazarus walks up to him first and tries to get him to side with him to scrap the mission, while Speedman walks up later and tries to do the same thing for him. Meanwhile, Cody and Tealeaf hit the drop point and see Cockburn's corpse, but are then captured by the renegades and taken to a heroin processing plant.
Speedman and Lazarus share a moment where they talk about Speedman's performance in Simple Jack, and how he went "full retard" without getting more into his character. Lazarus and Chino also manage to get on each other's nerves while they're setting up camp, as Lazarus may be too much into his black character. Meanwhile, Portnoy loses his "jelly beans" to a flying bat, and chases it around ferociously.
In the midst of crossing the river, Lazarus takes the map from Speedman and tells him he's abandoning the movie. Speedman, not in the mood to lose his career, opts to continue making it the best way he can. He splits up from the other actors and departs on his own route. Later that evening, he sets up a makeshift shed, watching a rerun of Star Trek on his Ipod. He hears something rumbling in the distance and finds himself confronting a bear, which he stabs violently. He looks to see it's a panda bear, which sends him into deep shock because he worked in a campaign months before where he helped panda bears.
The next morning, Speedman calls up Peck on his satellite phone, the one he hid earlier. He's using the panda skin as some sort of gear. He explains what he's killed, and after a humorous conversation where Peck thinks he's killed a hooker, he explains what happened. Meanwhile, the renegades sneak up behind him and knock him out, dragging him and his cell phone back to the heroin plant.
Meanwhile, the rest of the actors continue on their own path, with Portnoy tripping out from the lack of his "jelly beans" and Chino and Lazarus continuing to get on each other's nerves. Portnoy runs into an ox and considers skinning it to make himself a leotard. They go over a hillside to see that they've run into the heroin processing plant, where the others are being held. They see Speedman getting tortured, but he thinks it's an act and keeps yelling "CUT!" as he rises and lowers into a pool of water.
Speedman is then dragged into the main headquarters, where the warlord, a 12-year old kid named Tran (Brandon Soo Hoo) discovers who he is while beating him. It turns out that the dealers watch Simple Jack quite often, and are enlightened by it. They decide to hold Speedman for ransom. They call up his agent, who goes to pay Grossman a visit. However, he's unaware it's for a ransom demand. (He still thinks it's about the TiVo.)
Upon calling in with ransom demands, Grossman refuses to budge. He yells out obscenities and hangs up, then explains to Peck why they no longer need Grossman. He even offers a private jet and a lot of money as a bribe to make Peck forget about him. Then he and his assistant break out in a silly dance to celebrate Speedman's departure. Peck begins to wonder about his moral standing with not only his client, but one of his closest friends.
As Speedman is forced to re-enact Simple Jack for the heroin crew's local dwellers (using someone else's teeth, no less), the rest of the actors decide to mount a rescue mission to save him and the others. They start to pack it in for the night to rest up. Portnoy is tied to a tree, since he's having more of his hallucinations. It turns out that the "jelly beans" were in fact pieces of heroin, which kept him going through his Fatties movies. Chino accidentally reveals that he's gay, but then switches right back to his subject of "loving pussy". Sandusky wishes he had met Jennifer Love Hewitt, a woman that Lazarus dated a while back.
The next morning, Lazarus makes his way to the gate with Portnoy hiding under a cloth and an ox. They let him in, since he speaks fluent Chinese. Meanwhile, Sandusky and Chino sneak in from behind, fake guns at the ready. Portnoy is cut down from the ox, and Lazarus goes to leave, but Tran notices an error in his story. When he demands a correction, Lazarus pulls out his fake guns and fires away, yelling, "I'm a lead farmer, mother fucker!" He has Chino watch over the soldiers while he, Portnoy and Sandusky find the others.
Sandusky frees Cody and Tealeaf, who was revealed at first to have hooks for hands but in fact has his real hands. It's revealed that he's a fake, but he wrote the story in a tribute to his fellow soldiers. Cody grabs all his explosive gear. Meanwhile, the soldiers pick up their guns and begin firing at Chino like crazy.
Lazarus locates Speedman, but he's been put into a new frame of mind. It turns out that a young kid gave him a wooden Oscar for his performance as Simple Jack, something that's been missing in real life. In return, he's adopted the kid, calling him Half Squat.
Meanwhile, Portnoy gets into a huge fight with Tran. Tran kicks his ass for the most part, but then Portnoy grabs him and slams him through a railing, crashing onto the ground. He emerges to find a huge pile of heroin sitting in front of him, ripe for the picking.
Cody manages to blow up a building to distract the soldiers while Tealeaf makes a run for the chopper. Sandusky runs into Portnoy while he attempts to touch the heroin. He explains that he doesn't really need it, but Portnoy's tired of being laughed at and grabs two big handfuls. Two soldiers run into the room to confront them. Portnoy farts, making them laugh. He knocks them both out with the handfuls of heroin and grabs a weapon.
Lazarus and Speedman begin arguing back and forth about who they really are. At this point, Lazarus finally breaks out of character, horribly upset. The others show up and manage to convince them to leave, even though Speedman's still in his current frame of mind. They load into a truck and begin speeding away from the village, but Tran comes with a rocket launcher, which he fires at them. The rocket blows up the truck, but everyone survives. They start to get Sandusky out of it, and Speedman snaps back to reality.
They make their way to the chopper just as Cody finishes rigging the bridge with explosives. They all get in, except for Speedman, who is convinced he can work things out with the locals. He makes his way back, only to turn right around with Half Squat on his shoulders. When he discovers the kid trying to stab him, he throws him off the bridge into the water. Tealeaf blows up the bridge just as Speedman makes his way across, but he's wounded and lands just short of the chopper. Lazarus gets out and consoles him, just as he did in the beginning of the movie. This time, however, he's showing real tears.
Tran and his soldiers, still alive after the bridge blowing up, come out of the woodwork as Lazarus and Speedman load up into the chopper. Tran prepares to fire his rocket launcher again when Peck comes running out of nowhere, holding a TiVo unit. Tran fires, but Peck throws the unit between the rocket and the helicopter, blowing it up. The helicopter flies away as Peck goes running off into the woods.
Everyone has a happy ending. Speedman finally gets an Oscar (from Lazarus, no less) for his performance in a film based on the events that happened during filming. In the audience, Chino gives a big hug to his new gay boyfriend (Lance Bass), while Sandusky gives a kiss to his date -- Jennifer Love Hewitt. Grossman and his aide watch on TV, mockingly applauding and rolling in the success. The exec goes off to "take all the credit" as Grossman tells him that a "nutless monkey" could do his job. He then breaks out into a dance as the credits roll.
By the way, it's revealed that Peck makes it safe and sound. He's on a chartered flight sipping away at a drink. Grossman concludes his ridiculous dance and the movie ends.