In "The Guest," the prisoner is an arab who is accused of murder. The French gendarme Balducci says:
We had been looking for him for a month, but they were hiding him. He killed his cousin.
Daru's charge, then, is to harbor the prisoner for one night and then deliver him to the prison the next day. Rather than condemn the arab, who has done him no harm, Daru feels obligated to leave him at the crossroads between prison and freedom.
Ironically, the prisoner chooses prison. Does he feel guilt for his crime and, therefore, punish himself by going to prison. Does he fear freedom? Does he honor his host Daru by carrying out the mission Daru could not? In the end, the prisoner is just that: a prisoner to his lack of freedom. He chooses death instead of freedom, which Camus believes is what he believes of most humans.