It is in the future, and a technology has been developed to record a human personality onto a computer, so it can be downloaded into another brain later. The recorded consciousness, or persona, retains all the memories and personality of the original, but when placed in the new brain it has no access to any motor functions. It experiences everything the host personality does, and can communicate mentally with it, but it cannot seize control. It is only along for the ride.

It is a form of immortality. You can continue living vicariously, albeit in another body, but only as an observer and confidante. The persona only remembers its former life until the day it was recorded. The procedure becomes very popular for those who can afford it, and people have themselves uploaded to storage media so that if they should die, they can continue as a persona in another host. Folks have themselves repeatedly recorded, usually once or twice a year, but by law, all previous copies of their personality are destroyed. Supposedly, there is only one "backup copy" per person.

Of course, not everyone observes the law, and there is a brisk trade in bootleg personae, as in-demand tapes of famous people are not destroyed, but bought and sold on a thriving black market. In especially high demand are scientists, artists, financiers, and others whose personae provide status, as well as advice. Hosts collect them for prestige, or to give themselves a high powered advisor and counselor.

Silverberg explores every possible permutation of this bizarre world,
including variations like people who carry more than one persona inside them, and the rare case where a persona actually takes over its host. The persona has no access to motor functions, but it is capable of psychologically intimidating a weak-willed host, essentially nagging and bullying it into doing what it wants.

Brains with personae can be recorded, and the persona survives, so potential immortality is assured as long as you faithfully record your brain patterns every now and then. And if you die unexpectedly, you wake up in another brain, but without any recollection of any of the events you experienced between the time you were last recorded and the time you died.

Silverberg had a great time with this one.