Fujiko is at a prison with less security and no one tries to escape. reason why is because those who escape will get killed by one of these deadly machines called Iron Lizards(Land Sharks). Fujiko sends a letter to Lupin telling him to help her out of the mess she's in. So Lupin, Jigen, and Goemon robbed a bank and let themselves get caught. So that way they can enter the prison without any trouble. But it'll be a lot of trouble when they try to escape with 3 Land Sharks programmed to kill them.
—J LeGault