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!
- The Daleks make a fake, hollow copy of the Pentaray.
- The Pentaray can be transported on top of an aircraft.
- While the story may be known as The Penta Ray Factor, the actual device within the story is named "Pentaray".
- 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 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 were finally seen doing this until TV: Remembrance of the Daleks