Key to a Mystery is the 32nd episode of the 2013 series of Calimero.
In this episode, a mysterious intruder is trying to get into Do Vinci's workshop, but the kids can't get past Calimero's mom to get to the secret entrance. How can they stop the intruder?
This episode can be watched here: http://www.cartooncrazy.me/watch/calimero-2014-episode-32-key-to-a-mystery/