"A lone prisoner" can mean a single prisoner, not necessarily alone in the prison. You are the "lone" individual with the power, but you are not the "lone" individual in the prisoner perhaps?
Maybe you are among a group of civil war prisoners being transported from your village, after suffering under the oppression of the ruthless (and sometimes omniscient) imperial guard when a dragon swoops down and wipes everyone out, leaving you to wander the icy mountains alone in your wrist irons.
...nah, probably you have to escape from some sewers again so you can do a tutorial with rats hehehe