At the Multicorp Ecology Center in New Jersey, a team of armed mercenaries disguised as clowns bursts into Dr. Randall Pierce's Bio-Enhancement Division. They are not there for Pierce himself — their target is the gorilla he has been treating, a super-strong creature encased in strength-augmenting armor. Despite Pierce's warnings that the animal is still in pain and could turn violent, the intruders tranquilize it and haul it away. Pierce recognizes that these men, though dressed as buffoons, are professional soldiers.
Meanwhile, at Multicorp's Fifth Avenue headquarters, the corporation's public face is all smiles: CEO Adam Frost is hosting a charity event and presenting a $50,000 check to an environmental group called Fresh Air. When Pierce corners Frost to report the break-in, Frost shuts him down. Calling the police or the press would be a scandal that could tarnish Multicorp's carefully polished image, and Frost refuses to allow it. Pierce is told to say nothing and do nothing. Furious but powerless, Pierce returns to his lab — where he finds his son Ricky waiting for him with a bag from Tastee Burger. A clown mascot on the wrapper is the spitting image of the mercenaries who raided the lab. Pierce quickly realizes that Tastee Burger is owned by Flex Corporation, the same company linked to illegal rainforest clearance in the Amazon Basin. That is almost certainly where they have taken the gorilla.
Pierce is wracked with guilt. He created the bio-enhancement technology, and now his own invention is being used as a weapon against the environment he meant to protect. Ricky pushes his father to act, pointing out that Pierce himself preached taking responsibility for one's actions. Reluctantly, Pierce agrees to a test run: he will equip the five remaining animals in his lab with their bio-armor suits and neuro-enhancement helmets, giving them human-level intelligence and combat capabilities. A dolphin, a kangaroo, a lion, a bear, and a bald eagle are fitted with their gear. Awkward and bickering from the start — the lion and the bear immediately argue over who should lead — the team adopts the name Brute Force. Pierce makes clear this is a one-time trial: perform well, and they keep the suits.
With help from Phil, a contact at Fresh Air, Pierce and Brute Force fly to the Amazon Basin in a small prop plane. Phil drops them as close to Flex's clearance operation as he dares before distracting customs, leaving the team on their own. Brute Force deploy from the plane arguing over leadership and code names — the eagle insists on being called Soar rather than Slipstream, and the lion and bear continue to bicker — while Pierce quietly sighs. The dolphin, Surfstreek, still hasn't quite adapted to moving on land.
Brute Force quickly locates the gorilla in the custody of Flex mercenaries, who intend to use the armored creature to terrorize a native village that has resisted their bulldozers. The team charges in chaotically. The bear, Wreckless, fires her Bearzooka at full power — knocking out mercenaries but also damaging the eagle's armor and blowing up a patch of the very forest they came to save. The lion, Lionheart, gets punched by the gorilla and saved by Wreckless, who then tells him to get out of the way so she can handle it herself. The eagle, Soar, ditches her damaged armor mid-flight to catch a falling Lionheart. Hip Hop the kangaroo and Surfstreek mop up the remaining soldiers on the ground. The mercenaries' leader — the head clown from the lab raid — tries to flee but is stopped cold by Hip Hop. When the dust settles, the gorilla has slipped away and a bit of forest has been collateral damage, but the mercenaries are routed and the village is safe.
Pierce gives the team a grudging pass — they sent the mercenaries packing on their first outing — and tells them they have earned a second chance. As Pierce puzzles over an ultra-light metal-web uniform fragment left behind by the mercenary leader, back in New York the true villain reveals himself. It is Frost, acting behind Multicorp's green-friendly facade. He had hacked Pierce's research files before the raid to steal the neuro-enhancement data, and has now used it to build his own team of armored animals: Heavy Metal. With the gorilla soon to be added to their ranks, Frost declares that nothing — not Pierce and his "pathetic pets" — will stop him from seizing the money and power he craves.
Excelsioring your collection