Blackie has a friend named Joe Joe, and he needs the help that only Blackie can give. As a go between, Blackie goes to Farraday to warn of a planned prison break. Going out on a limb, Farraday follows through on the tip, only to learn there is no prison break, and the prisoner in question is in the warden's office at the moment.

There actually is a break planned, and a prisoner is shot when a disagreement arises with the others. Jo Jo has been shot and the news of his killing hits the streets, and Blackie is on the job. The whole situation also isn't sitting well with Farraday, who investigates in his own style. Somehow, he is just in time to help the recently shot Boston Blackie. . With all the shootings, bodies, and tangled list of suspects, unraveling the matter of who is doing it is the mystery.

How can a man, still behind bars, be the killer? With Blackie laid up in bed, and Farraday on the job, is there any hope of finding the killer? Feeling better, Blackie takes a tour of the prison to see if he can figure out how the deeds have gone down. Even Farraday is on the track of fishy things happening at the prison.

Prisoners keep escaping, and returning to prison. By now, Blackie has the answers, and reveals a secret tunnel, and exposes the mystery.