When it is time for the monsters to give some of their old toys away for charity, Six does not want to give away her rocking horse Sparkles. When her siblings tell her she has to, she decides to run away not wanting to part with the toy. This results in a search around Centerville for Six and her toy rocking horse Sparkles. The other six monsters start to wonder if it was right for them to tell Six she had to give up Sparkles when she wasn't ready, but when events lead up to Six seeing Mary's little cousin, Carrey play with Sparkles, Six begins to cry when Sparkles was in the water, so she decides for herself that she is ready to give the toy up by letting Carrey keep it.
