The episode begins with Alex Browning, the school bus driver, parking his school bus outside a zoo. Taking attendance, he looks around to see Clear Rivers, Carter Horton, Sam Lawton, Molly Harper and Wendy Christensen, all excited for a day at the zoo (except Wendy, who is nervous as usual). The group enters the zoo, holding hands and singing a familiar tune, and walks up to a sign designating where everything is. While Alex ponders what they should look at first, the others scatter and run off to various parts of the zoo. Noticing the kids are gone, Alex runs after them.
Carter and Sam are standing by the baboon cage, poking the baboon with a stick and mocking it. The two run off laughing when Molly approaches, camera in hand. An exhausted Alex catches up to Molly, who asks Alex to take his photo with the baboon. Alex has Molly back all the way up to the cage, so that her body is pressed up against the bars. When Alex takes the photo, the flash from the bulb sparks something in the baboon, and as a result, the ferocious baboon begins attacking Molly in a gruesome manner.
Alex looks around and spots a blow dart gun and two tranquilizer darts in a glass case. Standing next to the case is Clear, who is eating an ice cream cone. Alex runs up to the case, grabs the little hammer hanging from the box, and gives it a hard swing. Unfortunately, the glass shards end up piercing Clear all over her face, making her scream in extreme agony. Realizing he has two problems to deal with now, he focuses his attention towards Molly when the baboon begins tearing her limb from limb. Alex quickly shoves a dart into the blow dart gun, and aims it at the baboon. He shoots the dart, but the baboon does not stop his rampage. It turns out that he hit Clear, who was stumbling in pain due to the glass shards piercing her face. Because of this, she ends up falling into a snake pit, where a snake advances on her.
Alex tries once more to try and knock out the baboon, but as he is too panicked to pay attention, he unknowingly places the dart into the blow dart gun backwards. He takes a big breath, but the suction of his inhale causes the dart to fly right into his throat, making him choke and eventually faint.
Several hours later, Alex wakes up, yawning and scratching himself (like he always would after sleeping) with the effects of the dart apparently wearing off. Suddenly, Alex remembers that Clear fell into the snake pit, and goes to check on her. Unfortunately, the snake that advanced on Clear has already eaten her, and is in mid-digestion. Alex jumps into the pit to save her, and after a brief struggle, Alex winds up getting eaten too. Fortunately, he is able to use his pen to cut the snake open and free himself. Unfortunately, the snake had already begun digesting Clear, as she is smothered in stomach acid. Realizing that there is nothing else that he can do for her, Alex runs off to find the others.
Elsewhere, Sam stands on all fours while Carter stands on his back and peers through a hole in a wooden fence. On the other side of the fence is a rhinoceros, which Carter pokes with a stick through the hole in the fence. After getting no reaction, Carter sharpens the end of the stick and begins poking the rhinoceros again. Still getting no reaction, Carter sticks a branding iron through the fence and brands a circle on the rhinoceros' skin, finally getting the animal's attention.
Alex runs up to the mischievous duo and Carter runs off, giving a mocking laugh. As Alex watches Carter leave, Sam asks Alex to lift him up so he can see the rhinoceros through the fence. Sighing, Alex agrees, much to Sam's delight. While running, Carter comes upon a helium tank used for inflating balloons and decides to have some fun. He inhales the helium, begins singing in a high-pitched voice and laughs about it.
Meanwhile, Alex hears Wendy shriek in the distance. While he turns his attention away, he does not notice the sound of approaching footsteps or Sam's head being impaled by the rhinoceros' horn through the fence. Determined to see what the problem is, Alex places a crate under Sam's feet and runs off, still not aware that Sam's head has been stabbed. The rhinoceros removes its horn from the fence and Sam falls down, dead.
Wendy is now seen bellowing in terror as a cute little baby chick cheeps and hops over to her, trying to get some love. Alex runs over to tell her everything is okay, but he accidentally and unknowingly steps on the chick. This causes Wendy to start yelling even more. Alex picks her up and runs off, stepping on and killing multiple chicks as he runs. Later he slips, crushing numerous chicks and covering both himself and Wendy with blood and the remains of dead chicks.
Carter has finally had enough fun playing with the helium and starts to walk off. He stops when he sees the baboon, who has escaped from his cage and is now playing with Molly's camera. He looks over at Carter and gets angry, wanting revenge for the humiliation he suffered earlier. Carter turns to run away, but he slams his eye into the nozzle of the helium tank. He is unable to get his eye free as helium flows from the tank to his head. His head slowly expands as his screams get higher and higher pitched until they stop altogether. Now dead, one of Carter' eyes begins to float up as though it were a long balloon (presumably a 260 balloon to be more specific).
The baboon runs off as Alex approaches, still carrying a traumatized Wendy. He sees the balloons and decides to get one for Wendy, Unknowingly, he grabs Carter' inflated eye, mistaking it for a balloon, and makes a balloon animal out of it. He hands it to Wendy, who stops crying and slowly smiles. He picks her up and carries her off. Unfortunately, Wendy realizes that the "balloon" she is holding is the nerve of Carter' eye, and because of this, she gives one last scream just before passing out.
Back on the bus, an exhausted Alex plops down in the driver's seat and looks around, taking attendance again. He is surprised to see Clear, Carter, and Sam laying dead, a traumatized Wendy, and the baboon holding Molly's camera. Alex looks suspiciously at the baboon until it places Molly's glasses on. Alex shrugs, either thinking the baboon is Molly or not caring, and drives off. From outside, we see a silhouette of the bus. Seconds later, a bright light flashes from the camera through the bus's windows and the baboon begins screeching. As the iris closes in completely, we hear the bus crash.