Who Blackmailed the Myna?

The Mynah has received a letter forcing him to give up some of his delicious strawberries if he ever wants to see his joke book again. Sherlock and Hermione investigate to find the blackmailer. The Orangutan? Penguin? Skunk? During the investigation, Sherlock is obsessed with a little game taught to him by his old master Ball of Purity which is supposed to bring him wisdom and concentration.