In this episode, Russell, Kai and Ella ask: How does a key open a lock? With help from beautiful Belle, the sound neuron, Nina and the children look inside a lock to see all the moving parts before leaving the workshop to visit a huge bank vault. The Inventors have all sorts of fun finding out why keys have teeth and they finish by making their very own locks.

Originally released by BBC Worldwide Learning, 2009. Streaming video file encoded with permission for digital streaming by Infobase on September 22, 2020.