A day of new discoveries! Caillou loses his voice, finds a frog in his throat, and finds other neat ways to communicate, until the frog goes away. Later on, Caillou is missing one of his favorite socks. He searches the house, and accidentally locks himself in the basement. Daddy comes to the rescue - only he locks himself in the basement too. All is well when Mommy saves them both and finds the missing sock. Then, Caillou, Rosie and Julie, their babysitter, go on a scavenger hunt.