Frank pays Okla a visit.
Recall that Frank had gotten himself into serious trouble while in prison, and, as he tells the story to Jessie, we can safely conclude that he was kept from being killed during an incident that occurred while he was incarcerated (the 'Captain Morphis' incident), by some sort of miracle. The actual miracle occurred not at the point when Frank was facing Morphis, but instead later, when Frank walked out into the open prison yard thinking he was going to be killed by the other inmates, as a result of the incident. The reason this miracle came about was because Okla was acting as a guardian angel for Frank. A guardian angel is an angel assigned to protect and guide a particular person. In addition to protecting Frank, Okla acted as his guide, in that he taught Frank everything he knows about safe-cracking (recall that Frank tells Jessie this during the diner conversation).
