While Splendid makes cake batter in the kitchen, Toothy is drawn to some chocolate chips on the counter. Splendid slaps his hand away, however, and assertively tells him he can't eat the ingredients before the party. He gets a peanut and cracks the shell, dropping the peanuts in a blender. He turns it on, but it stops because half of a peanut shell is stuck in the blender razor. Splendid reaches for the shell, but, remembering that the blender is still on, he unplugs the cord from the wall.
Seeing a peanut still in the shell, he tosses the peanut into his mouth. All of a sudden, it seems that he is superallergic to peanuts, because Splendid gets a purple rash all over his body, his lips swell up, and his body gets bloated. Toothy rushes over to help, but, spotting the chocolate, he pushes Splendid away and helps himself to a sugary treat. Later, as he leaves the hospital, Ribbons rides up on her unicycle and offers Splendid some peanuts. Hightower, the doctor, quickly slaps Ribbons' peanut bag to the ground, making her get mad and run off to find another snack.
Back at the house, Splendid, Buckethead, Rocky, Toothy, Pierce, Ribbons, and Braze decorate the place for a party. Pierce puts up a game of pin the tail on the donkey, not knowing that it's upside down, Braze fills a barrel with water for apple bobbing, Ribbons blows up balloons, and Toothy pours extra sugar in the punch, thinking it's not sweet enough. As they finish their preparations, Splendid sees someone coming towards the house and tells everyone to be quiet. Pierce turns off the lights shortly before the door opens.
When the lights are turned back on, we see Rip standing in the doorway while everyone shouts "SURPRISE!" Shocked by this, Rip is startled, but luckily he doesn't flip out. Everybody sings "For He's a Jolly Good Fellow" as Splendid brings Rip his birthday cake, causing Rip to shed a tear of happiness. He makes a wish and blows out the candles, while Pierce begins playing pin the tail on the donkey. Splendid hands Rip a cake knife to cut the cake, leading him to almost flip out. Fortunately, he snaps out of it and begins cutting the cake.
Toothy, now standing next to a pile of sugar covering the punch bowl, consumes a drop of sugar. He gets an intense sugar rush and begins spinning like a tornado. The tornado he forms sucks some peanuts out of Ribbons' hand and causes them to fly into Splendid's mouth as he's about to eat the first slice of cake. He suffers the same allergic reaction he did earlier, popping the balloons with his fur as he bloats up. Mistaking the popping noises for gunshots, Rip flips out into murder mode.
First he attacks Rocky by cutting part of his face with the cake cutter. He places the slice of face on Buckethead's plate before tying some balloons around his neck. Rip lets go of them and Buckethead flies into a ceiling fan where he is shredded to pieces. Next, as the spinning Toothy approaches him, Rip holds out the cutter and slices Toothy like an apple. Rip now turns his attention to Ribbons who is reaching for peanuts in the blender, oblivious to all that has gone on around her. Rip plugs the blender into the wall and shoves Ribbons into the blender, where she is ground into a bloody mush.
Braze, seeing everything that has happened, hides in the water barrel. Rip searches for more victims to kill when his gaze comes upon Braze poking out of the barrel. He puts the lid on the barrel, almost drowning Braze who attempts to escape. Rip begins sticking knives, forks, and other sharp objects through the barrel, narrowly missing Braze's body and draining the water. Braze breathes a sigh of relief, but Rip takes the barrel outside and rolls it down a hill. The barrel breaks upon hitting a tree and a dismembered and bloody Braze flies out in numerous directions.
Pierce, still unaware of what is going on, walks towards the still bloated Splendid. As he pokes Splendid in the eye with the tack on the tail, he explodes, bringing Rip out of his flipped out state. He looks over to see Pierce impaled on the wall by many of Splendis's fur. Not seeming to notice (or at least care about) the death and destruction around him, Rip uses one of Ribbons' ears to mix the fluid in the blender's jar, which comprises of Ribbons' blood and the peanuts from earlier. Upon drinking the fluid, he gets the same allergic reaction Splendid did. As the iris closes to end the episode, his lips are caught in the hole and cut off, which then has blood coming out of the lips as they fall.