This novel was originally published in 1971. However, the only thing that really dates are the computers. They store data on tapes, and the user inserts the tape into a slot, very much like an eight-track cassette.
The main character is a prisoner on a barren planet. The only thing he can remember is his name, Andas Kastor. He has a small window, but otherwise he is in a kind of solitary confinement. The guards are all robots. However, one day an electrical storm passes over the prison, and lightning hits it.
All of a sudden Andas remembers that he is an imperial prince and a human of African descent. He lives on the planet of Inyanga, home planet of the Dinganian Empire. Apparently, some sort of memory inhibitor was in place. The door to his cell is no longer locked, and he opens it. The first person he sees is a female, although she is not human. Her skin is covered with scales, and her hair is green. He introduces himself, and she informs him that she is Elys of Posedonia. They both speak Basic, the common interstellar language. Then they meet a Salariki, which is a feline species. His name is Yolyos. There are three other prisoners, Hison Grasty, an obese native of the planet Thrisk, Ilyas Tsiwon, a human of Naul, and Turpyn, a mutated human who was a boss of the Thieves' Guild. The robots who served as guards and servants are as motionless as statues. They learn that all six were on the verge of becoming very powerful. Andas's grandfather, for instance, was close to death, and Andas was first in line for the throne. They also determine that their most recent memories were all in different years. For Andas, it has been 45 Earth years since his most recent memory. Turpyn is the only one who has a clue as to what happened, and even he is not sure. He thinks that they have all been abducted, and that androids have taken their places.
They discover that Turpyn is an expert at picking locks and set him on the task of opening all files and drawers to find anything useful. Fortunately for them, a supply ship arrives, and they capture it. Again, Turpyn has the most technical knowledge, so he becomes the leader. Although it is completely computerized, it does have crew quarters for four, which makes a tight fit for the six of them. They find computer tapes for voyages to other planets on the ship. One of them was for Inyanga and another for Naul. Andas argues in favor of traveling to Inyanga and Tsiwon for Naul. Since none of them have a coin, the rig a robot to draw one of the tapes at random. It chooses Inyanga. After loading as much food as the ship could hold, they take off.
Their flight is monotonous, and several of them have trouble adjusting to weightlessness. At least the ship is able to go directly from the surface of a planet with an atmosphere to hyperspace. Andas finds himself making friend with Yolyos. However, when they land, they are definitely not on Inyanga.
It turned out that Turpyn had switched tapes and brought them to a secret base of the Guild. He is first one to exit the ship, but he finds to his disappointment that the base has been abandoned and taken over by a jungle into which he escapes. Elys has been suffering from dehydration, so they find a pool of water into which they immerse her. After a few hours, she is back to normal. They return to the ship, only to find that Tsiwon is dying of an apparent heart attack. Elys has had the most medical training, so she is assigned to care for him. One of the cardinal space laws is that you never abandon someone on a planet, so they wait all night for Turpyn to return. The following morning, Yolyos and Andas search for him. They discover that Turpyn had become dinner for one of the local predators and bury what remains were left. When they return, they learned that Tsiwon has died as well. After burying him as well, they take off for Inyanga.
They land at a secret base in the desert. Presumably the owners of the spaceship use it for smuggling and other illegal purposes, but are not present this day. In a nearby cave, they discover skimmers, a kind of air ship. Andas decides to leave at night in order to navigate by the stars. The others elect to join him rather than take another chance with the ship. Elys becomes dehydrated again, so one of the first priorities is to find a body of water. By dawn, Andas finds a river, so Elys is able to rejuvenate herself. They spend the rest of the day hiding.
Andas's plan is to enter the imperial palace, known as the Triple Towers, during the night at one of the secret entrances he remembers. He hopes they are still there and still secret. Then he can reconnoiter and find out the political situation, especially whether there is an android double of him on the throne. Unfortunately, he crashes his skimmer when they arrive at the palace, and it is a total wreck. However, no one is seriously hurt, and they land where he wants. He finds a secret entrance, gets everyone inside, and reaches a hiding place. After securing their hidden room, he leaves the others and moves down a secret passageway. He eventually comes to a spy hole in a secret door with a view of a bedchamber. After a time, three women enter the room, two of them clearly servants. After sending the two servants away, the third woman addresses Andas and threatens him. Somehow she has detected him and is retrieving a ring when he opens the door to stop her from using it. When he has her in his grip, he asks her the name of the emperor. She replies that it is Andas of the house of Kastor and her father! After tying her up and taking her ring, Andas leaves the room by way of the secret door. He goes further down the secret passageway in the hope of find the emperor's bedchamber, which he finally does. He is alone when he enters, so he searches for and finds a special key in the same hiding place where it was in forty-five years previously. Then the emperor enters, and Andas looks into his own face, only forty-five years older. The emperor addresses Andas and accuses him of being the android, since he has aged and Andas has not and since he has three daughters. Andas does not know whether to believe him and has no trouble overpowering him and escaping into the secret passage.
He retraces his steps as he makes his way back to the others. However, he encounters Yolyos, who tells him that Grasty has been killed and Elys captured by the guards. He leads Yolyos into a part of the palace where people had been known to disappear without a trace and was the least likely to have any guards. Andas discovers the reason for the disappearances is that there is a portal into a parallel universe. Having nothing to lose, Andas and Yolyos plunge into it, and then their adventures really begin.
This report prepared by Thomas R Feller