Who Fooled the Hippopotamus?

A mysterious character has called Mr. Hippo to put in an emergency order for a large wooden dresser. But when Hippo shows up at the address, there's no one there. He's been fooled and won't get paid. Who did it? In the meantime, Hermione has had enough of trying to get in touch with Sherlock and offers him a smartphone. Will he learn how to use it, considering he hates technology?