Chip Off The Old Chip is the thirtieth episode of Season 3.
Timmy wants to participate in the school musical, so he can be with and can impress Trixie. He wishes for Chip Skylark’s dreamy voice… and gets the leading part! Unfortunately, Chip now has Timmy’s voice, which causes his career to take an immediate nosedive. Timmy feels bad that he caused Chip these problems, but he cannot wish because his voice is not a child's voice anymore. How will Timmy manage his desire to impress Trixie and his desire to save Chip?
At school, when Timmy and his friends are hearing Mr. Bickles talking about a school play, Timmy thinks it is boring, until Mr. Bickles says that Trixie is acting in the play. At home, Timmy is practicing his singing. Unfortunately, Timmy's singing is so horrible that it breaks Cosmo and Wanda's fishbowl. Wanda questions Timmy's horrible voice since Timmy is normally a good singer, Timmy explains that it's probably due to Trixie being in the play, so he is nervous and that makes his voice horrible.
Not sure what to do, Timmy then watches TV and he sees Chip Skylark singing so great that it repairs Cosmo and Wanda's broken fishbowl. Timmy then wishes to have Chip Skylark's voice and gets an enjoyable voice. Unbeknownst to Timmy, his natural voice went to Chip Skylark. Timmy thanks Wanda, and practices with Chip's voice by singing, fixing the fishbowl. Suddenly Timmy's parents rush into his room thinking they heard Chip Skylark, but they only see Timmy. Timmy's parents then become depressed thinking that what they heard was just Timmy. As they leave, Mrs. Turner questions why she couldn't have given birth to Chip Skylark.
At school, Mr. Bickles and Trixie cannot find anybody to participate in the musical, until Timmy comes and sings. His voice is so wonderful that it repairs the broken picture. He gives Timmy the lead role. Meanwhile, Teeth TV wants to make Timmy Turner the "New Chip Skylark." A news report shows Chip poorly singing the National anthem at Bankee Stadium. The crowd booed and threw heavy wet sponges and even bricks at Chip. Chet Ubetcha announces that Chip Skylark's voice stinks. Realizing this, Timmy then asks Cosmo and Wanda why Chip got his voice saying that he only wanted his voice, and not exchanging them. Cosmo and Wanda say they know, but his voice had to go somewhere, and Chip Skylark was the only person who's mouth is open. Unfortunately, Timmy could not wish his voice back because Da Rules stated that vocal wishes had to be done in the voice of the godchild the godparents were assigned to. When confronted with the question of what should we do next, they turn to television where they get the answer to split up; one godparent would stay with Timmy while the other would be with Chip Skylark and listen for any cues that would lead him to Timmy Turner.
Sure enough, while Chip Skylark sat gloating about his awful voice and how no one liked him, he wished for a job and got one as a "Poorly Sung Pizza Delivery Boy". Meanwhile as an audience of hundreds shows up at the school musical, Timmy Turner realizes he is in a no-win situation. If he stayed in the dressing room, he would not get this opportunity to sing alongside Trixie and if he went out into the audience and performed, the "New Chip Skylark would be stuck being the old Timmy Turner". After Chip shows up, they turn to television for what should they do next and they turn to television. On stage, a Wheel Of Coincidence is shown saying the words GET CHIP SKYLARK TO SAY I WISH I HAD T_MMY TURNERS VOICE, but instead of Timmy it's Tommy.
Meanwhile, Mr. Turner approached the depressed Chip sitting down and tells him about his dream of being a better singer than Chip. When the play started, Timmy arrived in a nick of time. Trixie, tied up in a chair, was excited for his arrival, until Timmy Turner decides to recite the pledge of allegiance and do what TV said. After Chip repeated Timmy saying "I wish I had Chip Skylark's voice.", the wish was granted as the voices were put back where they belong. Chip starts to sing Find Your Voice, as it being the finale for the play. Everybody is overjoyed, except Trixie as she glares at Timmy for having Chip upstaging her. She refuses to forgive Timmy and leaves while being tied up.
Timmy is glad that everything is back to normal, even though he lost the part in the play. Cosmo proofed up a giant TV as it shows Mr. Turner, being interviewed by Brad, horribly sings for Timmy, leaving the three (Timmy, Cosmo, and Wanda) that were hearing this bald.