In the city of Bulos on the planet Solturis, Lurr tries to warn King Redlin that the Daleks are coming to wipe them out. He has seen it all in his Bowl of Tomorrow. Redlin will not believe him. But the Daleks have already landed...
King Redlin ignores Lurr's warnings that strange creatures are on their way to attack the planet. Eventually, spacecrafts land outside the city of Bulos. The Daleks convince the King that they are peaceful explorers of space and they have landed to make repairs. In reality, the Dalek Emperor wants to use the opportunity to learn of any weapons within the city that can be used against them. They learn of the Pentaray and plan to steal it to eradicate Bulos.
Lurr learns of the Dalek plan with the Bowl of Tomorrow and warns his granddaughter Mirva. He sends Mirva to warn Prince Jareth and they find that the Pentaray had already been stolen. The King states the Daleks need the key to activate the Pentaray but he finds it has been stolen as well. Meanwhile, Lurr's treacherous cousin Geltis approached the Daleks and offers them the key. They arrange to the mountains where they plan to use the Pentaray on Bulos. Lurr learns of his cousin's actions but Geltis stabs him and blows up his equipment along with any incriminating evidence. He flies back to the mountain, intent on betraying the Daleks too and taking over the city.
The Emperor instructs all but two ships to depart and continue the conquest of other planets. Some of the Daleks remaining on Solturis are destroyed by Geltis using the Pentaray and he then proceeds to aim it at Bulos. Jareth throws a rock at him and sends him plummeting to his death. The remaining Daleks begin attacking Bulos with their own weapons but before they can attack from above, Jareth wipes them out with the Pentaray. With Solturis safe, the Dalek Emperor, watching from deep space, makes an exception to the Dalek law of destroying what they cannot conquer, for the fleet has received a message from Skaro, stating they must return immediately!
- TV 21's special correspondent for psychic affairs, which deal with happenings outside normal human experience, is sure that scientists' claims of seeing ghosts are true. They go on to say that it would be odd if an old castle like Tracking Station 17, with all its history, was not haunted.
- Lieutenant Fisher, stand-in controller at Marineville, has ordered high speed fire launches to Tracking Station 17 after recieving reports of explosions in the computer room.
- Space City reports that a May-day alert in area 23 was picked up by a Martian radio observatory. XL5 is believed to be investigating.
- People are fleeing from New York as animals grow to fantastic size. Garbled reports from the Press Agency talk of frogs twenty-five feet high and mass battles between twelve-foot rats and twenty-foot cats. The World Army is rushing tanks and troops to the area.
- Hans Beula has broken the Universe 100 metres record at the Astra Stadium on Venus, recording a time of 8.7 seconds.
- A message from Senior Special Agent 009 begins "Cyanide sprang trap. Gun battle outside the Cathedral. Have followed the fleeing agent to a Yorkshire steel town".
- While the story may be known as The Penta Ray Factor, the actual device within the story is called "Pentaray".
- The Daleks are called back to Skaro, leading into the next story.
- During the final attack on Bulos, one Dalek orders the others to "ascend to hover position". Daleks would not do so on screen until Remembrance of the Daleks more than twenty years later.
- The final page of The Penta Ray Factor was seen on the back of an in-universe issue of TV Century 21 magazine in the Thunderbirds episode The Man From MI.5.
- In 2005, Altered Vistas released an animated adaptation of this story.
- Terry Nation's Dalek Annual 1977 as The Envoys of Evil
- Doctor Who Weekly 37-39 in black and white
- Doctor Who Classic Comics 2-3 in colour
- DWMS The Dalek Chronicles in colour as The Penta Ray Factor.
- The Daleks invade Solturis. (COMIC: The Amaryll Challenge)
- The Emperor is called back to Skaro. (COMIC: Plague of Death)