Sherlock Holmes and the Deadly Necklace (1962) – on imdb as Valley of Fear.
For a start I don’t quite know why it was released as Valley of Fear, because it hasn’t got a Valley of Fear in it, unless you start getting allegorical.
Also the necklace isn’t deadly. And no, it’s not a clever name. It’s just a necklace that was stolen from an archaeological dig in another country by a thief, who then stole it from the person who wanted it stolen. The person who wanted it stolen steals it back, so Sherlock Holmes breaks in and steals it, so that the police can send it to be sold at auction, except it gets stolen on the way to auction, except it’s stolen from those thieves by Sherlock Holmes and finally posted to himself at a totally different address just in time to be auctioned to someone completely new who will probably have it stolen off him in the very near future.
All clear? Elementary.
Oh, just to say that we watched the Rifftrax version so you might want to do the same if you’ve got any chance of unpicking any of the plot at all.