You would presumably be able to create derivative works based on Steamboat Willie, but not reference things that happen in things that are still under copyright, as is the case with Sherlock Holmes (<a href="http:&#x2F;&#x2F;io9.gizmodo.com&#x2F;us-judge-rules-sherlock-holmes-and-watson-are-in-the-pu-1490854362" rel="nofollow">http:&#x2F;&#x2F;io9.gizmodo.com&#x2F;us-judge-rules-sherlock-holmes-and-wa...</a>)