Brain and Francine use fake love notes to get vengeance against Muffy after her science project gets more credit. Their joke has unintended consequences, which means they must fix it before things get worse. When D.W. saves a little boy from getting hit by a car with her whistle, she becomes an overzealous safety control freak. Arthur and his friends try to stop her from ruining the upcoming soapbox race, while D.W. learns the hard way that her obsession with finding everyone else's safety faults causes her to jeopardize her own safety.