When the Tibble twins get a set of drums and decide to perform the Summer Serenade Festival, D.W. wishes that she has an instrument of her own to play, and, with inspiration from Arthur, Buster, Francine, and Fern, she ultimately creates her own kinetic instrument. Arthur and Buster go to investigate a rumor that tigers are loose in the park. This turns out to be an experiment by Brain, who wanted to see if anyone would believe a seemingly true internet rumor with no leads. Brain's story leads to Arthur and Buster solving a mystery about dogs disappearing from the park.