Who Cemented the Turtle?

Turtle is the card dealer at Baboon's café. One morning, she calls Sherlock in an emergency. Someone has cemented her shell so she can't get her feet out of it. Three unhappy customers who have lost a lot of money become the suspects. Who is the criminal? In the meantime, Sherlock has received a gift from Ball of Purity: small fortune cookies containing an incomprehensible message.