Burt meets Jack Costello after many years. Burt is a boxer and he is fleeing after a fixed match that he should have lost but instead he won. Then he vanishes. Costello finds in his office Burt's son, 'Jo-Jo' Ritchie, who had came because his father had ordered him to go to him. Then Jo-Jo cames back to Groggy where he lives and when the two of them are dining, two men arrive and kill Groggy. Jo-Jo runs away and Extralarge sets on finding him and his father.

Agent Blake finds the corpse of a child. It is one of a long chain. The murderer is called The Miami Killer by the newspapers. Extralarge assists the police in their investigation. All the murdered children suffered from some kind of ailment and the murderer knew his or her victims very well. The successive victim appears to be Elsie who is asthmatic and Extralarge suspects father Marthy and Elsie's teacher. Then Elsie is kidnapped. Can she be saved?

A scientist arrives in Miami on a ship coming from Cuba. Detectives Extralarge and Willy have been hired to protect him. The scientist, however, is killed under their eyes without them being able to do anything about it...