Plot[]
Ms. Appleby announces her class' last assignment of the year: A ten minute presentation on any language in pairs. She reluctantly agrees that Bulk and Skull can do English, but points out they need to do more than mindlessly babble. Later, Tommy and Billy inform Aisha they're planning to do Ancient Egyptian hieroglyphics. Kat arrives with the assistant for her and Aisha's project: A chimpanzee named Kelly brought over by her aunt, who is lecturing at the local university. Kat and Aisha are planning to teach her basic sign language. Observing the chimp, Rita Repulsa is mainly interested in winding up Goldar about their similarity but Lord Zedd thinks it is an opportunity.
At the juice bar, Lieutenant Stone assigns Bulk and Skull to solve a theft: Bananas, which were meant to have been delivered to Ernie. Exiting, they see the four teens with Kelly, who eats a banana, and realize she could help them track down the thief. Seeing the four Rangers have taken Kelly to a secluded spot, Zedd decides to act and sends Finster and a group of Tengas down. Tommy, Billy, Kat and Aisha transform into Ninja Ranger forms to battle the Tengas, while Finster tries to shoot Kelly with a weapon that will turn her into a monster. The chimp evades him and Kat chases him off, with the Tengas also retreating.
Kat and Aisha take Kelly back to Aisha's place, but she wanders off while they are getting a snack. Bulk and Skull entice her with a banana and she leads them to a fruit seller. The fruit seller decides to adopt Kelly as a mascot, dressing her as a Rastafarian. Bulk and Skull think they have found their culprit. Furious at Finster's failure, Zedd personally turns Kelly into a monster, the Sinister Simian. Bulk, Skull and the fruit seller flee as the monster rampages through the park.
Zordon summons Kat and Aisha to join the other Rangers at the Command Center and shows them the Simian. Kat is worried about hurting Kelly and Billy suggests he could find a cure if he had a sample of her fur. The Rangers morph and teleport to the park. Kat's voice seems to calm the Simian at first, but when Billy tries to get a sample, she strikes him. After a brief battle, Kat and Aisha manage to restrain the Sinister Simian long enough for Billy to get the sample and teleport back to his lab.
Tommy, Kat, Aisha, Rocky and Adam try to keep the Sinister Simian contained while Billy works on a way to administer a cure. Zedd and Rita grow the Simian to giant size. Billy returns: He has loaded his cure in a projectile that can be fired from the Shogunzords, but hasn't had a chance to test it. The Rangers summon their Zords and battle the Simian, but Billy is unable to get a clear shot. Tommy gets the Sinister Simian's attention by having the White Shogunzord make ape-like movements that arouse her curiosity. Billy fires the projectile and the Simian shrinks away. The teens find Kelly in the park unharmed. Zedd blames Rita for the plan's failure while she argues he did no better.
Later, the six teens are at the juice bar, with Rocky and Adam congratulating Kat and Aisha on their project. Bulk and Skull drag in the fruit seller and tell Ernie they've caught the banana bandit. When Ernie gets a word in edgeways, he reveals he found the bananas: The new delivery guy put them in the freezer. The fruit seller says they'll hear from his attorney. Kelly goes over and gives Bulk a kiss.